Support file completion inside #include's

[lorin]

It would be great if SuperTab supported file-based tab completion inside of C/C++ style #include "filename.h" statements.

For example implementation, see http://stackoverflow.com/a/22536695/742

[ervandew]

Instead of patching supertab, you can also add new contexts as defined in the help.

It might be nice to create an 'autoload/supertab/contrib' folder in supertab where custom file type specific contexts like this can reside which users can then utilize if they want. I'll think about this some more and perhaps do that with a c/c++ include context as the first one.