Fix issues discovered by common python linters

Fix some issues discovered by common python linters including:
* switch `None` comparisons to use `is` rather than `==`. Identity !=
equality, and I've spent 40+ hours before tracking down a subtle bug
caused by exactly this issue. Note that this may introduce a problem if
one of the scripts is depending on this behavior, in which case the
comparison should be changed to `True`/`False` rather than `None`.
* Use `except Exception:` as bare `except:` statements have been
discouraged for years. Ideally for some of these we'd examine if there
were specific exceptions that should be caught, but for now I simply
caught all. Again, this could introduce very subtle behavioral changes
under Python 2, but IIUC, that was all fixed in Python 3, so safe to
move to `except Exception:`.
* Use more idiomatic `if not x in y`--> `if x not in y`
* Use more idiomatic 2 blank lines. I only did this at the beginning,
until I realized how overwhelming this was going to be to apply, then I
stopped.
* Add a TODO where an undefined function name is called, so will fail
whenever that code is run.
* Add more idiomatic spacing around `:`. This is also only partially
cleaned up, as I gave up when I saw how `asn2wrs.py` was clearly
infatuated with the construct.
* Various other small cleanups, removed some trailing whitespace and
improper indentation that wasn't a multiple of 4, etc.

There is still _much_ to do, but I haven't been heavily involved with
this project before, so thought this was a sufficient amount to put up
and see what the feedback is.

Linters that I have enabled which highlighted some of these issues
include:
* `pylint`
* `flake8`
* `pycodestyle`

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