Cleaned .gitignore

Removed unnecessary stuff and left only *.class and *.ctxt
Added "doc/" to .gitignore

The doc directory stores any documentation files, which are unnecessary
to keep and can be easily made using only the code.
Added Interfaces package

The Interfaces package contains interfaces that will be implemented in
the final project.
Merge pull request #1 from CombustibleLemon/master

Combine with CombustibleLemon