[Feature] API for yam.set()

[runspired]

It looks as though yam used to have the ability to write as well as to read variables. 6fce91e

I'm working on a PR for ember-cli-cordova that will require storing a configuration setting in .ember-cli when the main blueprint generation is done.

It would add both a namespace (cordova) and a setting (multiEnv):

   cordova : {
       multiEnv : true
   }

Is .set() a feature that we could bring back? It does obviously make yam a little more clunky to avoid stripping comments, but it would be great to have a lib for writing to config files from ember-addons.

[selvagsz]

👍 for this feature. Curious to know the reason behind the removal of .set ?