Rename SemImply to SemImplied

[alyst]

Renaming SemImply to SemImplied (and imply field to implied, imply() call to implied() usw) can potentially resolve some confusion.
imply is a verb, so it implies that the imply() call does some action, or that SemImply are some kind of callable objects, whereas imply() is just the accessor method, and SemImply is not callable.
Also, the docs refer to them as "imply types", and I often find myself stumbling over the grammar of such sentences, because on the first read I treat "imply" as a predicate.
With "implied" there should be less confusion, also SemImplied/implied would have a nice complementarity to SemObserved/observed.

[Maximilian-Stefan-Ernst]

Thanks, added to the list for v0.3.0.