updated all file headers to 2019
Introduced a printf function (apalDbgPrintf()) to the periphAL interface.
Slightly enhanced documentation of newly introduced apalSPITrabsmitAndReceive() function.
add apalSPITransmitAndReceive function to templates/periphAL.h
Adapted all file headers to state that this work is licensed under LGPLv3 (fromerly GPLv3).
Initial open-source release.