Make :compiler and :go keys expand build matrix
Make :compiler and :go keys expand build matrix

For upcoming C, and C++ support that will support switching between GCC and Clang.
Go support will start with a single runtime, I am adding it proactively, just like we
did before with :jdk.

developerfm/travis-core,kidaa/travis-core,kidaa/travis-core,final-ci/travis-core,travis-ci/travis-core,travis-ci/travis-core,kidaa/travis-core,developerfm/travis-core,GistIcon/travis-core,developerfm/travis-core,GistIcon/travis-core,jantman/travis-core,travis-ci/travis-core,Tiger66639/travis-core,final-ci/travis-core,Tiger66639/travis-core,GistIcon/travis-core,travis-repos/travis-core,jantman/travis-core,final-ci/travis-core,travis-repos/travis-core,Tiger66639/travis-core