Cleaned up travis.yml

Added/edited comments, tried to make sure gcov likend properly(may be unnecessary)

I left GCCVER="-4.8" as we require the '-', so I swithched downloading g++-4.8 to requireing CC="gcc"
Can get around this by using a user-config.jam for gcc to invoke g++-4.8

TODO:
1. clean up jamfiles
2. pull request and merge the new buildsystem
3. remove dependencies