a big round of makefile improvements & fixes

tested on NetBSD, FreeBSD, macOS with pkgsrc, and macOS with Bmake

Merge pull request librsync#144 from dbaarda/dev/release-v2.0.2

Release v2.0.2

Merge pull request librsync#128 from dbaarda/doc/release-v2.0.1

Release v2.0.1.

Bump version to 2.0.0 to match soname

Fixes librsync#48.

Release 1.0.1

Add release date