Added more tests for path completion and shell command completion

[tleonhardt]

Also:

• Added a test for do_pause
• Cleaned up a bunch of magic numbers from existing test for shell and path command completion

This closes #109

[codecov]

Codecov Report

Merging #160 into master will increase coverage by 0.69%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #160      +/-   ##
==========================================
+ Coverage   90.23%   90.93%   +0.69%     
==========================================
  Files           1        1              
  Lines        1147     1147              
==========================================
+ Hits         1035     1043       +8     
+ Misses        112      104       -8

Impacted Files	Coverage Δ
cmd2.py	90.93% <0%> (+0.69%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a4ded9f...e968c41. Read the comment docs.