Use scan-build in automated CI

Unfortunately, for the time being there is no way to
make the build matrix not go crazy, so the current infrastructure
results in 6 builds :( It's not the end of the world though, since
this project isn't as busy as it could be. Testing to see how horrible
this is now.
Don't tell scan-build which compiler to use!

Unfortunately it seems to be freaking out about this right now,
will have to investigate.
Fix scan-build complains in Format/StringBuilder

The utf8BOM complaint is a bit weird, because it is clearly not
a bug. But I'm not sure how to get scan-build to ignore certain
things just yet, so this will take some investigating.
Don't scan 3rd-party libs
Merge pull request #3 from caitp/issue-3

Run Clang's ScanBuild on Travis-CI