REF: command line to make optional deps truly optional

[klauer]

Also refactors such that testing can be done more effectively, and tools more easily usable by Python (interpreting kwargs and not argparse namespaces).

• Removes ability to use pytmc-db et al, pushing users toward the subcommand usage: pytmc db.

Closes #87

[codecov-io]

Codecov Report

Merging #89 into master will decrease coverage by 1.03%. The diff coverage is 70.4%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
- Coverage   77.46%   76.42%   -1.04%     
==========================================
  Files          10       14       +4     
  Lines        1216     1506     +290     
==========================================
+ Hits          942     1151     +209     
- Misses        274      355      +81

Impacted Files	Coverage Δ
pytmc/bin/xmltranslate.py	88% <100%> (ø)
pytmc/bin/summary.py	87.9% <100%> (+15.31%)	:arrow_up:
pytmc/bin/debug.py	53.37% <58.33%> (ø)
pytmc/bin/stcmd.py	58.58% <59.25%> (-5.31%)	:arrow_down:
pytmc/bin/types.py	51.76% <60%> (ø)
pytmc/bin/pytmc.py	80% <73.33%> (ø)
pytmc/bin/db.py	45.83% <75%> (+20.83%)	:arrow_up:
... and 6 more

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[klauer]

Agreed on the coverage concerns, @teddyrendahl. Looking into it locally: (previous results vs current)

It seems like the addition of the submodules in the coverage report was enough to bring it down?

[teddyrendahl]

I believe you might just be being punished for testing files that were not imported below. I'm fine with merging as is.