This is a lazy workaround: 4c9a241949067fc8d55f3ea12170ad364bd8b18d
is amended to do nothing on python2, so we have the same issue that
was present before. This allows the code to execute, and hopefully
almost nobody is using python2 code anyway.

f868a56b935b6152d611b22f7a5538f14dafb194 is amended in the same way.
For python2 code we have the same lack of timezone-awareness as before.

This allows the tests to pass under python 2.7.

Support realtime cutoff access

"after some quick testing, the execution time got halved (32-ish
seconds to 16-ish seconds) when going through all journal entries."

Closes #63.

Add log namespace support which is added since systemd v245

This change enables to add extra fields to JournalHandler in a
configuration file loaded by `logging.config.fileConfig`, which only allows positional
parameters:

class=systemd.journal.JournalHandler
args={'level': INFO, 'SYSLOG_IDENTIFIER': 'my-cool-app'}

[zj: originally the patch added a new positional parameter to
__init__(), but that is not backwards compatible. So I added a new
classmethod to allow the positional parameters to be passed.]

`strftime("%s")` is not in the official python documentation but in my system (ubuntu 18.04 python 3.6.9) it is not aware of the object timezone and will return the wrong value if the timezone is specified and is not the system local one.

There are multiple ways to ensure a python `datetime.datetime` is in local timezone, the easiest (with python 3.3+) is to call `.astimezone()` If one wants to support earlier versions of python an extra dependency might be needed like `dateutil.tz.tzlocal()`.

We get <systemd.journal.JournalHandler object at ...> in older versions,
and <JournalHandler (NOTSET)> in since Python 3.6.
https://github.com/python/cpython/commit/c0752011472790e34d171b89f4b862cc3fd8ad08

send() already does conversions in a type-specific way, and doing it
in journal handler would defeat those conversions. In particular, UUIDs
would be converted to early and have dashes.