Issue#3 trajpt base class

There are still no methods for actually setting values, but this starts to build ideas and functionality we need. Fixes issue #3.
I'm not sure we need to document the implemented virtual methods.  Doxygen will do this by default ( http://www.stack.nl/~dimitri/doxygen/manual/config.html#cfg_inherit_docs ).  When using an interface definition (like we are), the behavior of the implemented method should match the interface documented behavior.