Unit test coverage for transcripts from history

[kotfu]

• Add unit tests for transcripts generated by the history command.
• Make implementation more robust (it doesn't have to read from disk now, just write)
• Fix 'history -t' doesn't handle multiline commands properly #384 and Transcript generation and/or testing is broken #385, new issues discovered during unit testing
• Add unit test coverage per request in Improve code coverage of unit tests #268

[codecov]

Codecov Report

Merging #387 into master will increase coverage by 0.59%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master     #387      +/-   ##
==========================================
+ Coverage   88.98%   89.58%   +0.59%     
==========================================
  Files           8        8              
  Lines        2615     2630      +15     
==========================================
+ Hits         2327     2356      +29     
+ Misses        288      274      -14

Impacted Files	Coverage Δ
cmd2/cmd2.py	90.81% <96.66%> (+0.91%)	⬆️

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[tleonhardt]

Thanks for refactoring and improving this.

[tleonhardt]

Thanks for fixing these