Changelog for beetbox#93 (and version bump)

Changelog for beetbox#89

Version bump: 2.1.6

Version is 2.1.5

Fix beetbox#32: ffmpeg interference with stdin stream

Merge pull request beetbox#30 from beetbox/modern-glib

Fix warnings in beetbox#24

Delete pipeline object (close beetbox#28, close beetbox#29)

Fix ReST formatting in the README

This was preventing rendering on the PyPI page.

Version bump: 2.1.0

Remove Future Work section

This is why we have Issues.