Support requiring multiple inputs for a single command

[CoolOppo]

For example, let's say you are bundling together JS files:

There needs to be a way to specify for a rule that all matching files are required for the single rule. Maybe something like this:

[bundle]
from = '(?P<name>.*)\.min\.js$'
require-all = true
to = './bundle.min.js'
command = 'cat $i >> $o'

(Obviously the cat command here isn't too great of an example since that would actually work without this feature. A better example is linking C .o files to an executable.)