Add testing framework based around LLVM's "lit.py".
Modifications to test_case.cpp contributed by Arun.
Currently, only test_case.cpp has been converted to use lit.
test_id will follow.

Signed-off-by: James Courtier-Dutton <James@superbug.co.uk>
Signed-off-by: Arun Prakash Jana <engineerarun@gmail.com>
Minor fix to documents.