Document Reader Subsystem

Context

Add documentation for the Reader subsystem classes and for how to add new device implementations.

Summary

Documentation was added to the classes and members that will be included in the hosted documentation.

I moved LecroyHdfFile to /old to remove it from the inheritance diagram in Doxygen.

I also made some minor changes to variable names to make them more consistent and I fixed an error I found with the vector of channels being returned from getNextChannels(). It was adding new channels at each iteration instead of replacing them.

How was this tested?

The compiled code runs as before, and I looked through the new documentation using make docs.