Add SCons build support to Hall A analyzer.

Notes:

1.  I changed .gitignore to be a little more inclusive of compilations on other platforms (like MacOSX), and added appropriate SCons ignores as well.
2.  The "local" version of scons (version 2.3.0) has modifications contained therein (esp. to ~/Tools/__init__.py) to allow shared library generation and softlinking which mimics what is currently done in the Makefile.