c_config: Allow `env` to be specified for check_conf
ndnx: new extra tool to configure NDNx and openssl
extras/ndnx: Adding check for openssl library compatibility
Tools/python: Extending python tool to show more command-line arguments to control which python is used and where py/pyext files should be installed

The new options are in addition to the existing PYTHON, PYTHONDIR, and
PYTHONARCHDIR, providing help messages to the user, so it can easily
change parameters without second-guessing of what are they.

Environmental parameters override command line arguments (is it right?)

Also, this commit includes extension to Configure.find_command that
allows to specify name of the searched command. This is helpful when
search command is a huge list, as in case of python's python-config case.
Tools/python: Don't specify prefix for get_python_lib, since this way it would result in a wrong PYTHONDIR and PYTHONARCHDIR on certain platforms
Tools/python: Changing logic with byte-compilation of python files

Now, files are compiled during build stage, not install stage