move unit tests at the projects root

which is a more conventional place.
rename main.py into more explicit name run_test.py
refactor the code in run_test to be import as a module
and run the tests with a function calling.
 tests has moved to project root
add sphynx documentation
add target test in setup.py

the target test run unit test from the newly build moby_exec_engine
builded library. the mobyle2.lib project need to be intalled first

the tests can be run from src vesion using directly tests/run_test.py

  python setup.py test -vv  run tests using build/lib package
  python tests/run_tests -vv run tests using mobyle_exec package