Fixup: Mayfly throws assertions_failed from REQUIRE, make it expected.
Update VERSIONS.md.
Add a facility to run functions closer to actual exit than atexit().
Refactor subprocess runner.
Add "(in <filename> at line <line>)" to assertion messages.
Stylistic change in VERSIONS.md.
Bump version number to 0.1.2.
Merge branch 'release/0.1.2'