Allow for more granular documentation parsing

Apologies if this issue has already been raised! I did not see it when searching but I might have just not searched hard enough :)

Right now, including documentation when parsing is a simple bool that applies for the crate I am generating for as well as any dependencies I might be including. However, I might want to have short documentation for dependencies, or no documentation for dependencies, or a mix and match where I want documentation for some dependencies but not others. If it was possible to define documentation parsing on a per-dependency basis, that would be much appreciated!

Start by locating the configuration and dependency-parsing paths that currently use the single documentation boolean. Define how documentation settings should apply to the generated crate and to each dependency, then verify that users can select short, absent, or included documentation independently for dependencies.