Shared Library Changes for Release 2.1.2

Shared library libddcutil is backwardly compatible with the one in ddcutil 2.0.0. The SONAME is unchanged as The released library file is

It also fixes several minor bugs and has internal changes to better accomodate the proprietary Nvidia diver

Changed Functions Comments
ddca_start_watch_displays  Requires that all video drivers implement DRM
ddca_get_sleep_multiplier  Revert to release 2.0.0 semantics
ddca_set_sleep_multiplier  Revert to release 2.0.0 semantics