support more than strings and lists in from-dep's with-attributes

[bhearsum]

Right now, from-dep supports matching arbitrary values if they are part of a list of values, but only matching strings when directly defined. For example, you can do this:

from-deps:
  with-attributes:
    foo: [true]

But not:

from-deps:
  with-attributes:
    foo: true

We should probably be more lenient about the types of values we allow outside of the list, or more restrictive about what's allowed in the list. (I suggest that all basic types should be allowed in both places.)