Added parameter for path to JSON_to_CPP.py

set path through --path that is the root directory for the code. The
default is None as this was the previous behavior, however this does not
make sense.

Also the path name is normalised as, depending on OS there is confusion
on slash direction.
Path

generate_headers.py may not be called from the correct path, so get the
path of generate_headers.py and determine the base path from there
assuming generate_headers.py will be in dev/
Merge pull request #25 from Rod-Persky/python-args

Added parameter for path to JSON_to_CPP.py