Documentation improvements for abc module classes

Document most methods in abc module classes.

Also fix obvious error (with compiler warning) in still-unused Windows-
only abc::module_impl_base::use_count() method.
Improve documentation for abc::numeric

Document functions in abc::numeric.
Work around bug in MSC16’s __VA_ARGS__ expansion

Add [DOC:1829 __VA_ARGS__ MSC16 bug] and macro ABC_1829(), respectively
documenting and working around a baffling confirmed bug in MSC16. Every
variadic macro expanding __VA_ARGS__ had to be changed to use ABC_1829().

Changes tested to also work in GCC.
Remove unnecessary default template argument values

Not supported by MSC16 and not needed in the current codebase, so they can
go.
Merge branch 'master' into vs2010