Improve help output

[waf]

Two changes to help text:

• Add clear to the help output (helps address #262)
• Shorten some of the description text in the --help output. Changes to active voice rather than passive voice. Shortening the text helps avoid wrapping when run in the terminal; the wrapping makes it harder to understand the help output as the alignment is off.

[codecov[bot]]

Codecov Report

Merging #276 (1d4fbab) into main (4a74e55) will decrease coverage by 0.1%. The diff coverage is 91.6%.

@@           Coverage Diff           @@
##            main    #276     +/-   ##
=======================================
- Coverage   77.5%   77.5%   -0.1%     
=======================================
  Files         81      81             
  Lines       5475    5478      +3     
  Branches     720     721      +1     
=======================================
+ Hits        4246    4248      +2     
  Misses       965     965             
- Partials     264     265      +1     

Impacted Files	Coverage Δ
CSharpRepl/ReadEvalPrintLoop.cs	90.7% <75.0%> (-0.6%)	:arrow_down:
CSharpRepl/CommandLine.cs	94.4% <100.0%> (ø)