discord 2.0.2 backward compatible, add optional FLAC support

There are no changes to discord itself in this release.

This version of the discord package includes a patched libsndfile that will allow FLAC support. It can only be statically linked to prevent issues with dynamic libraries already installed. Also included is the package libsamplerate.

The workaround text has been updated for the latest alsa-lib version, and the README has instructions about how to get FLAC support into discord.