The stand-alone driver / test suite needs a better naming convention

[mnlevy1981]

Keeping everything related to the standalone driver in the test/ subdirectory doesn't really make sense, nor do the current contents of regression_tests/ (call_compute_subroutines/ really is a regression test, and gen_settings_file/ could probably be turned into one fairly easily, but everything else is effectively generating documentation). I suggest the following:

1. rename tests/ -> standalone_MARBL
2. Under standalone_MARBL/, keep driver_exe/, driver_src/, input_files/, obj/, and python_for_tests/
3. Move bld_tests/, regression_tests/, and unit_tests/ to a new standalone_MARBL/tests/ subdirectory
4. Create a new standalone_MARBL/tests/doc_gen/ subdirectory

It would be great to tie doc_gen/ subdirectories into the actual generation of the HTML documentation, though I don't know how feasible that is.

Some thoughts that might be worth considering:

1. Maybe driver_exe/ and obj/ belong in a standalone_MARBL/bld_out/ subdirectory or something
2. Rename standalone_MARBL/driver_src -> standalone_MARBL/src?
3. standalone_driver/ instead of standalone_MARBL/? The point is that no external GCM is needed for anything under this directory, it's meant to provide simple test cases and examples