mraa: add common hpp

* Wraps some of the C functions that libmraa has into the mraa namespace
* Not included in swig bindings as of yet

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>
types.h: add missing asterix from comment.

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>