Move Jekyll::DEFAULTS to Jekyll::Configuration::DEFAULTS
Add Jekyll::Configuration
Jekyll.configuration should use the new Jekyll::Configuration class
TomDoc Jekyll::Configuration
Unit test for Configuration#stringify_keys
Add unit tests for Configuration#config_files
In Configuration#config_files, cascade to the Configuration's value of 'source' before the default
Refactor setup block for test of Configuration#config_files
Added a unit test for Configuration#backwards_compatibilize
Moving the backwards-compatibilizing to Configuration#read_config_files. @mattr-
Refactored Configuration#config_files
Add 'excerpt' page variable to Docs Variables page.
Moved 'excerpt' var below 'title'.
Merge pull request #953 from mojombo/refactor-configuration

Refactor Jekyll Configuration
Merge pull request #956 from jhauraw/doc-var-excerpt

Add 'excerpt' page variable to Docs Variables page.