Rename `playslave++` to `playd`.

Fixes #23.

Mostly global find-and-replaces.  Initial pass, may need additional
ones.  Compiles on MSVC, to check on others.
changed tar.gz to playd in gitignore
Merge pull request #25 from UniversityRadioYork/mw-playd

Rename `playslave++` to `playd`.