Porting new configuration format

It includes some refactor code to share the code between new and old
configuration format routine.
Support json array / object in new configuration format
Extract Config::Element into fluent/config/element.rb
Support array / hash in DSL
Remove unused code and handle incomplete hash / array object correctly
Add RSpec and several specs
Add 'allow_comments' option
Fix the symbol value spec
NewParser renamed to V1Parser and change related names
Move Config.xxx_value helpers to fleunt/config/types.rb
Merge pull request #293 from fluent/use-new-config

Add --use-v1-config option to enable new configuration format