Prettied up the README with syntax highlighting.

[ci skip]

README.markdown

@@ -21,13 +21,17 @@ For the moment, Arel uses Active Record's connection adapters to connect to the
 
 Generating a query with Arel is simple. For example, in order to produce
 
-    SELECT * FROM users
+```sql
+SELECT * FROM users
+```
 
 you construct a table relation and convert it to sql:
 
-    users = Arel::Table.new(:users)
-    query = users.project(Arel.sql('*'))
-    query.to_sql
+```ruby
+users = Arel::Table.new(:users)
+query = users.project(Arel.sql('*'))
+query.to_sql
+```
 
 ### More Sophisticated Queries
 
@@ -35,45 +39,65 @@ Here is a whirlwind tour through the most common relational operators. These wil
 
 First is the 'restriction' operator, `where`:
 
-    users.where(users[:name].eq('amy'))
-    # => SELECT * FROM users WHERE users.name = 'amy'
+```ruby
+users.where(users[:name].eq('amy'))
+# => SELECT * FROM users WHERE users.name = 'amy'
+```
 
 What would, in SQL, be part of the `SELECT` clause is called in Arel a `projection`:
 
-    users.project(users[:id]) # => SELECT users.id FROM users
+```ruby
+users.project(users[:id])
+# => SELECT users.id FROM users
+```
 
 Joins resemble SQL strongly:
 
-    users.join(photos).on(users[:id].eq(photos[:user_id]))
-    # => SELECT * FROM users INNER JOIN photos ON users.id = photos.user_id
+```ruby
+users.join(photos).on(users[:id].eq(photos[:user_id]))
+# => SELECT * FROM users INNER JOIN photos ON users.id = photos.user_id
+```
 
 What are called `LIMIT` and `OFFSET` in SQL are called `take` and `skip` in Arel:
 
-    users.take(5) # => SELECT * FROM users LIMIT 5
-    users.skip(4) # => SELECT * FROM users OFFSET 4
+```ruby
+users.take(5) # => SELECT * FROM users LIMIT 5
+users.skip(4) # => SELECT * FROM users OFFSET 4
+```
 
 `GROUP BY` is called `group`:
 
-    users.project(users[:name]).group(users[:name]) # => SELECT users.name FROM users GROUP BY users.name
+```ruby
+users.project(users[:name]).group(users[:name])
+# => SELECT users.name FROM users GROUP BY users.name
+```
 
 The best property of the Relational Algebra is its "composability", or closure under all operations. For example, to restrict AND project, just "chain" the method invocations:
 
-    users                                 \
-      .where(users[:name].eq('amy'))      \
-      .project(users[:id])                \
-    # => SELECT users.id FROM users WHERE users.name = 'amy'
+```ruby
+users                                 \
+  .where(users[:name].eq('amy'))      \
+  .project(users[:id])                \
+# => SELECT users.id FROM users WHERE users.name = 'amy'
+```
 
 All operators are chainable in this way, and they are chainable any number of times, in any order.
 
-    users.where(users[:name].eq('bob')).where(users[:age].lt(25))
+```ruby
+users.where(users[:name].eq('bob')).where(users[:age].lt(25))
+```
 
 Of course, many of the operators take multiple arguments, so the last example can be written more tersely:
 
-    users.where(users[:name].eq('bob'), users[:age].lt(25))
+```ruby
+users.where(users[:name].eq('bob'), users[:age].lt(25))
+```
 
 The `OR` operator works like this:
 
-    users.where(users[:name].eq('bob').or(users[:age].lt(25)))
+```ruby
+users.where(users[:name].eq('bob').or(users[:age].lt(25)))
+```
 
 The `AND` operator behaves similarly.
 
@@ -85,38 +109,51 @@ The examples above are fairly simple and other libraries match or come close to
 
 Suppose we have a table `products` with prices in different currencies. And we have a table `currency_rates`, of constantly changing currency rates. In Arel:
 
-    products = Arel::Table.new(:products)
-    products.columns # => [products[:id], products[:name], products[:price], products[:currency_id]]
+```ruby
+products = Arel::Table.new(:products)
+products.columns
+# => [products[:id], products[:name], products[:price], products[:currency_id]]
 
-    currency_rates = Arel::Table.new(:currency_rates)
-    currency_rates.columns # => [currency_rates[:from_id], currency_rates[:to_id], currency_rates[:date], currency_rates[:rate]]
+currency_rates = Arel::Table.new(:currency_rates)
+currency_rates.columns
+# => [currency_rates[:from_id], currency_rates[:to_id], currency_rates[:date], currency_rates[:rate]]
+```
 
 Now, to order products by price in user preferred currency simply call:
 
-    products.
-      join(:currency_rates).on(products[:currency_id].eq(currency_rates[:from_id])).
-      where(currency_rates[:to_id].eq(user_preferred_currency), currency_rates[:date].eq(Date.today)).
-      order(products[:price] * currency_rates[:rate])
+```ruby
+products.
+  join(:currency_rates).on(products[:currency_id].eq(currency_rates[:from_id])).
+  where(currency_rates[:to_id].eq(user_preferred_currency), currency_rates[:date].eq(Date.today)).
+  order(products[:price] * currency_rates[:rate])
+```
 
 #### Complex Joins
 
 Where Arel really shines in its ability to handle complex joins and aggregations. As a first example, let's consider an "adjacency list", a tree represented in a table. Suppose we have a table `comments`, representing a threaded discussion:
 
-    comments = Arel::Table.new(:comments)
+```ruby
+comments = Arel::Table.new(:comments)
+```
 
 And this table has the following attributes:
 
-    comments.columns # => [comments[:id], comments[:body], comments[:parent_id]]
+```ruby
+comments.columns
+# => [comments[:id], comments[:body], comments[:parent_id]]
+```
 
 The `parent_id` column is a foreign key from the `comments` table to itself. Now, joining a table to itself requires aliasing in SQL. In fact, you may alias in Arel as well:
 
-    replies = comments.alias
-    comments_with_replies = \
-      comments.join(replies).on(replies[:parent_id].eq(comments[:id]))
-    # => SELECT * FROM comments INNER JOIN comments AS comments_2 WHERE comments_2.parent_id = comments.id
+```ruby
+replies = comments.alias
+comments_with_replies = \
+  comments.join(replies).on(replies[:parent_id].eq(comments[:id]))
+# => SELECT * FROM comments INNER JOIN comments AS comments_2 WHERE comments_2.parent_id = comments.id
+```
 
 This will return the first comment's reply's body.
 
 ### License
-    
+
 Arel is released under the [MIT License](http://opensource.org/licenses/MIT).