Support mixture of short and long argument names

[wburklund]

Renames GetArgumentHelp to GetArgumentInfo and marks GetArgumentHelp as obsolete.
Closes #15.

[codecov]

Codecov Report

Merging #44 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #44   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines         366    366           
=====================================
  Hits          366    366

Impacted Files	Coverage Δ
src/Utility.CommandLine.Arguments/Arguments.cs	100% <100%> (ø)	⬆️

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