C++ classes for selection parser symbol table.

C++ classes for selection parser symbol table.

Convert the implementation of selection parser symbol table to use C++
classes.
 - Removes a few exception safety issues that were present in the
   initialization, as well as direct prints to stderr.
 - Documentation now follows the new Doxygen layout.
 - Removes some underscore-prefixed global names.

Related to #655 and #880.

Change-Id: Iecb690fa2e413c9dc487aacffac62a248ea3867a