Added documentation for THcRawAdcHit.

Added channel to time coefficients to the Adc and Tdc raw hit classes.

This makes the code nicer and with less duplication in logic.

Along with that I had to correct all the call sites to the RawHodoHit in all the
classes that use it.

Added new class THcRawTdcHit.
RawShowerHit update.