add example timeline builder

[ssteinbach]

Adds a simple example that builds a timeline from scratch using a list of files and times as input.

• add a command line argument to take a path of where to put the resulting file
• add a more helpful docstring

[codecov-commenter]

Codecov Report

Merging #993 (3f8e914) into master (d33bf24) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #993   +/-   ##
=======================================
  Coverage   85.60%   85.60%           
=======================================
  Files         192      192           
  Lines       18331    18331           
  Branches     2056     2056           
=======================================
  Hits        15693    15693           
  Misses       2112     2112           
  Partials      526      526           

Flag	Coverage Δ
unittests	85.60% <ø> (ø)

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[meshula]

lgtm