Work around ruby/ruby#713.

Closes #1412
Support arbitrary identifiers in keyframes selectors.

Closes #1383
Preserve double-star comments in sass-convert.

Closes #1432
Add a mailmap to clean up references to my dead name.
Bump VERSION to 3.4.4.
adding appveyor configuration to this branch off stable
use a larger build matrix

new versions of Ruby (with DevKit) have been installed:
  - 1.9.3 x86 (C:\Ruby193 - default in PATH)
  - 2.0.0 x86 (C:\Ruby200)
  - 2.0.0 x64 (C:\Ruby200-x64)