std.math: Add upstream changes/fixes and simplify go derived code

This also starts the documentation effort for the math/ subdirectory.
The intent is to use this as a somewhat representative test-case for any
work on the documentation generator.
f94964cd05Marc Tiehuis committed on 5/1/2019, 6:13:33 AMparent7bbc8eb
5 files changedLine totals unavailable