Miscellaneous small fixes, new doc comments, and dead code removal from
the core library.
Removing hard-coded references to Stiletto types whose references are added to weaving targets.

This allows us to ILMerge the core library into the weaver, thereby
allowing us to run its validation logic during weaving.  By removing
hard-coded references, the weaving target keeps its existing reference to
Stiletto without gaining a reference to the weaver.
Automating ILMerge of Stiletto.Fody and the weaving of a new unit-test project.
Exempting strong-named assemblies and those that don't reference and use
Stiletto from weaving.  Fixing other minor nits.
Added a NuGet MSBuild project that assembles build artifacts for packaging.
Merging master in to local.
Xamarin.IOS activated, so now I can build Stiletto.IOS.  Enabled it for
packaging.