Improve environment setting

[scizzorz]

$ mold -a foo -a bar init

is quite tedious when you're using environments.

I'd suggest two additions:

$ mold init:foo:bar

which will append foo and bar to the environments list just for the init recipe, and:

$ mold +foo +bar init

which is just shorthand for -a foo and -a bar

[scizzorz]

Maybe a better option is to allow recipes to be parametrized, eg specifying a recipe as something like:

recipe deploy/$ENV/$COMPONENT {
    $ "echo $ENV $COMPONENT"
}