Refactor audio player, add retry timeout

Fixes #442.
Fix player retry logic

If retry is triggered once and openStream fails after that retry is
never set to false, resulting in an infinite loop that cannot be
interrupted by the user.
Makefile: remove dependency generation for *.d files

The %.d rule means that 'make clean' will try to generate dependency
files first. Let's use somem extra gcc flags to make this simpler.

Fixes Github Issue #468

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Makefile: Avoid double path separator (//)

Causes problems on Windows/Cygwin. Fixes #471.
Fix volume control with ffmpeg 2.3