Improve `-I` option support

Namely, add support for multiple arguments for the `-I` option. For
example:

  % pry -Ilib:../code/src

Where `:` is the delimiter for paths. In the example above `./lib` and
`../code/src` directories will be added to $LOAD_PATH array.

Also, there was a bug in Slop with respect to parsing of "fuzzy options
with arguments"[1]. It is fixed now, so the next version of Slop will
indirectly resolve our issue #674 (-r/--require doesn't behave like
irb's)[2].

And finally, wrap some very long lines in the "cli.rb" (this is just a
cosmetic change).

[1]: https://github.com/injekt/slop/issues/74
[2]: https://github.com/pry/pry/issues/674

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>

lib/pry/cli.rb

@@ -57,12 +57,18 @@ class Pry
       end
 
       def parse_options(args=ARGV.dup)
-        raise NoOptionsError, "No command line options defined! Use Pry::CLI.add_options to add command line options." if !options
+        unless options
+          raise NoOptionsError, "No command line options defined! Use Pry::CLI.add_options to add command line options."
+        end
 
         self.input_args = args
 
         opts = Slop.parse!(args, :help => true, :multiple_switches => false, &options)
-        option_processors.each { |processor| processor.call(opts) } if option_processors # option processors are optional
+
+        # Option processors are optional.
+        if option_processors
+          option_processors.each { |processor| processor.call(opts) }
+        end
 
         self
       end
@@ -139,8 +145,12 @@ Copyright (c) 2011 John Mair (banisterfiend)
     Pry.config.requires << file
   end
 
-  on :I, "Add a path to the $LOAD_PATH", :argument => true do |path|
-    $LOAD_PATH << path
+  on :I, "Add a path to the $LOAD_PATH", :argument => true, :as => Array, :delimiter => ":" do |load_path|
+    load_path.map! do |path|
+      /\A\.\// =~ path ? path : File.expand_path(path)
+    end
+
+    $LOAD_PATH.unshift(*load_path)
   end
 
   on :v, :version, "Display the Pry version" do