Allows using yaml config files and shorthand config option

[jmatsushita]

Hi there,

You might not like the added dependencies, but this is something I needed for my own project and II thought you might consider adding the feature!

Cheers,

Jun

[jmatsushita]

By the way, shorthand means that it's possible to do

metalsmith --config blah

And it will automatically look for blah.json blah.yml or blah.yaml files.

[jmatsushita]

Working on fixing tests.

[coveralls]

Coverage remained the same at 94.304% when pulling a1d6274 on contentascode:master into 8d7265e on segmentio:master.

[coveralls]

Coverage remained the same at 94.304% when pulling a1d6274 on contentascode:master into 8d7265e on segmentio:master.