chpldoc should document transitive (public) uses

[bradcray]

As a Chapel programmer, it'd be helpful if a module's chpldoc-generated page showed the public use clauses contained at module-scope so that I'm aware what symbols beyond the module itself I'm gaining access to. Ideally, this would be hyperlinked to the module / symbols in question.

For example, given:

module C_Lib {
  proc c_fn() { ... }
}

module Lib {
  proc fn() { c_fn(); }
}

If Lib...

• contained public use C_Lib, it'd be nice to see that in its docs and have C_Lib link to the chpldoc page for module C_Lib
• contained public use C_Lib only/except c_fn;, it'd be nice to see that in its docs, with C_Lib linking to module C_Lib's chpldoc page and c_fn linking to the entry for c_fn()
• if public use C_Lib ...; appeared within fn() itself, chpldoc shouldn't show anything (since it's local and therefore doesn't impact what I see.

[and ditto for import]