Yaml, more features

This PR adds support for more yaml types. To make the tests pass, it needs the fixed version of timestamp>rfc3339 from 622f333, but as discussed in https://github.com/slavapestov/factor/pull/1057 622f333 is just a proof of concept and is not meant to be merged in.

I can also modify the failing test to not use decimals and remove 622f333 if that's better ?