gnewline: use yaml.CLoader
gnewline: use yaml.CLoader

I hate this pattern where you have Foo and CFoo, and CFoo is a million
times faster, but also the documentation says stuff like:

> Note that there are some subtle (but not really significant)
> differences between pure Python and LibYAML based parsers and
> emitters.

Look, either the differences are not significant, in which case you
should automatically use the faster parser if available; or they are, in
which case you should document them!

wjt/fewerror,wjt/fewerror