Move gengetopt input files to m4 directory. This separates the gengetopt input directory from its output directory. All gengetopt m4 file are moved to the new m4/gengetopt directory. As a consequence of this cleanup, we may get rid of the .gitignore file for the generated ggo files, which is a good thing as it was hard to keep it up to date.
Add missing alsa_write.ggo to .gitignore. This file is generated.
Implement support for libao via the new ao writer. This adds support for another writer to paraslash. The new ao writer allows to play an audio stream via one of libao's output plugins. Two new configure options are provided and the documentation is updated accordingly.
Add option for activating new buffer tree code to para_recv and para_write. ATM this option is ignored.
Add ggo/.gitignore to hide derived ggo files.