Add support for Yet Another Makeup Language

[BarelyAPrincess]

Per your readme, I'm filing an issue to get support added for Yet Another Makeup Language files. .yaml is the official extension but people can't seem to agree and also use .yml. I was able to manually map yaml to the SCRIPT_STYLE but I feel it should be included by default. Reference: http://www.yaml.org/refcard.html. Thank you.