[Yaml-core] .yml vs .yaml

[Trans <tra...@gm...>]

I know when I asked about it last, I was informed that the official
extension for a generic YAML file was `.yaml`. I certainly have no
issue with that in itself. However, in the field it seems like
everyone (at least in the Ruby circles) is just using `.yml`. If this
is predominantly the case for large majority of YAML users, perhaps it
would be better to just accept it and make `.yml` official?

While it may not seem a big deal, when one is frequently programming
for YAML files, it is much less troublesome and easier on the eyes to
write:

  File.read('foo.yml')

then

  File.read(Dir.glob('foo.{yml,yaml}'))

all the time.