python: add systemd.id128 module

uuid.UUIDs are utilized to hold UUID values.
python: utilize uuid.UUID in logging
journalct: also print Python code in --new-id
python: build html docs using sphinx

Build instructions:
   make
   make DESTIDIR=/tmp/... install
   make DESTIDIR=/tmp/... sphinx-html sphinx-man sphinx-epub ...
systemd-python: add Journal class for reading journal
systemd-python: moved PyRun_String to journal.py code
systemd-python: MESSAGE_ID as UUID for Journal
systemd-python: move default call dicts from C to python
sphinx: document Journal class too
systemd-python: Journal log_level moved to python
systemd-python: implement this_boot/this_machine in Python
systemd-python: some python3 and bug fixes
systemd-python: Tidy up _reader error handling
systemd-python: Moved _reader datetime usage to python
systemd-python: updated _reader header to standard license
systemd-python: correct data_threshold error return value
systemd-python: _reader add_match takes single string

python code now takes care of multiple matches
systemd-python: Update _reader docstrings
systemd-python: _reader now takes unix timestamp in seconds
systemd-python: remove unneeded ifdef for query_unique