Rename "DEPRECATED" to "DISABLED"

Fix issue #817 (DEPRECATED: Use `edit` instead.)

Rename `CommandSet#deprecated_command` to `#disabled_command`. Rename
the file in "commands/", too.

lib/pry/command_set.rb

@@ -263,13 +263,13 @@ class Pry
       commands.delete(cmd.match)
     end
 
-    def deprecated_command(name_of_deprecated_command, deprecation_message, matcher=name_of_deprecated_command)
-      create_command name_of_deprecated_command do
+    def disabled_command(name_of_disabled_command, message, matcher=name_of_disabled_command)
+      create_command name_of_disabled_command do
         match matcher
         description ""
 
         define_method(:process) do
-          output.puts "DEPRECATED: #{deprecation_message}"
+          output.puts "DISABLED: #{message}"
         end
       end
     end

lib/pry/commands/deprecated_commands.rb

@@ -1,2 +0,0 @@
-Pry::Commands.deprecated_command("edit-method", "Use `edit` instead.")
-Pry::Commands.deprecated_command("show-command", "Use show-source [command_name] instead.")

lib/pry/commands/disabled_commands.rb

@@ -0,0 +1,2 @@
+Pry::Commands.disabled_command("edit-method", "Use `edit` instead.")
+Pry::Commands.disabled_command("show-command", "Use show-source [command_name] instead.")