Set up Travis so it runs make with both clang and gcc

[nickserv]

• Fixes Consider using CI (continuous integration) #38.
• You'll still need to sign in to Travis and enable this repository to finish setting up Travis. This PR only includes the configuration file and build status badge (which isn't activated yet).
• For now, this just runs make with both clang and gcc. The build will fail if there is an issue with either compiler. I'm assuming this is what we want.
• I'm not running make test on CI because it's currently broken. Fix "make test". Add Streem example file. #30 should fix this, then just change make to make test (which runs the make all task anyway).
• We still don't have unit tests. We probably don't need them yet, but that would be a good idea for the future.

[nickserv]

Thanks for merging! You should be able to enable Travis by visiting your profile and toggling matz/streem. I believe you'll still need to push again to trigger your first build, though.