Test doxygen file and function documentation on zsolve's main.

Note: Everytime we document a function that is at file or global scope
we must make sure to include that file for documentation using a
special \file command.  See here for details:
http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html#structuralcommands
doxyfy ZSolveAPI
Add binaries to gitignore
Make an Interface for Zsolve Algorithms

The former Algorithm was moved to ExtendedPottier.hpp, an
implementation of the new Algorithm Interface.
code documentation added
Give ValueTree its own file
Ignore some more test related files
Start work on ValueTree
Add simple gtest unittest framework