Player handling via opaque objects #13

Manage all aspects of omxplayer instances via struct player
opaque objects, thus encapsulating process creation, control pipes,
signals into new module player.c.

This will allow to prime a paused omxplayer with next track.
Allow up to 3 omxplayer instances #13

Which will even allow interrupting the playlist by a video,
and continue from the middle of the interrupted track.
Move IO utils to new utils.c #13
m_list: in memory playlist compiles #13

And the test case does not segfault. But that's all.