Update mixer volume when fppd starts. Issue #65.
When parameters are extracted from command line or setting file, the function setVolume is called.
In setVolume, command "amixer set PCM xx%" is performed to apply the volume.
In fppxml.php, send to fpp the real value (0-100), and not the value for amixer (50 to 100).
Add missing headers inclusion in settings.c
Merge pull request #66 from ihbar/SetVolumeAtStart

Update mixer volume when fppd starts. Issue #65.
Use sanitized value when setting the volume in setVolume()