Fix bug where ruby < 2.0.0 Range#size is not defined
Set PROTOC_VERSION to 2.5.0
Compile with protoc --plugin in spec_helper
Update gemspec, fixes activesupport < 1.9.3 dependency

* Add devin-c as gem author
* Remove java platform setting
* Remove gem extensions setting
* Constrain activesupport to < 4.0