Add RTF output option to tnefparse

[jrideout]

Changes:

• add an -rb command line option for rtf output
• Command line output when printing byte object bodies is now correct
• Correctly out the exit code on success and failure
• Optionally decompress the rtf file if compressed_rtf is present. This makes it a recommended, but not required dependency.

[jrideout]

The byte size difference between py2 and py3 is interesting. I'll figure it out.

[codecov]

Codecov Report

Merging #39 into master will increase coverage by 0.59%.
The diff coverage is 88.46%.

@@            Coverage Diff             @@
##           master      #39      +/-   ##
==========================================
+ Coverage   90.21%   90.81%   +0.59%     
==========================================
  Files           5        5              
  Lines         961      980      +19     
  Branches       93       97       +4     
==========================================
+ Hits          867      890      +23     
+ Misses         69       68       -1     
+ Partials       25       22       -3

Impacted Files	Coverage Δ
tnefparse/cmdline.py	85.07% <100%> (+13.14%)	⬆️
tnefparse/tnef.py	88.88% <75%> (-0.45%)	⬇️

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[petri]

Looks good to me. Thanks for the extra tests! Is it too much to ask to bring the patch test coverage up a notch more to satisfy our Codecov overlord? If there are no straightforward low-hanging approaches to do that, we can relax the Codecov patch requirement, at least in this case.

[jrideout]

The only thing that doesn't have coverage on the patch is testing the case of an ImportError when compressed_rtf is not installed. I think we should relax the Codecov patch requirement in this case.