the HMS calorimeter.

    Add src/THcShowerCluster.h.float, a version of THcShowerCluster
    class with float precision calculation in clX method.

memory consumption with event number.

       Add THcShowerClusterList::purge() method to purge and clean
       THcShower::fClusterList by the end of each event, in
       THcShower::Clear().

calorimeter.

Add list of clusters fClusterList in THcShower class.
Add method THcShower::GetShEnergy(THaTrack*).
Add method THcShowerClusterList::clear() in THcShowerCluster.h.

These were related to a) scope of some variable declarations, and b) use
of pre-increment vs. post-increment of non-primitive types (this has a
slight performance hit due to the way that pre- vs. post-increment
operators are overloaded in C++.

Also cleaned up a few places where initialized variables were not being
used.

Re-arrange, modify and make more detailed comments in the Shower*.h header
files. Add more comments in the Shower*.cxx files.