ury-playd v0.3.0 'Archway'

After a long hiatus, the next playd release is here for those of you who like releases.

This release changes much too much to mention, but here's the rundown:

• a completely new protocol (check the man page and other documentation for changes);
• a new CMake-based build system by @DinCahill, which should simplify building on Windows and in general;
• use of SDL2 to output sound, and libsndfile and libmpg123 to create it.