Added a unit test for custom intro when calling cmdloop()

[tleonhardt]

Also updated CHANGES.md

[codecov]

Codecov Report

Merging #181 into master will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #181      +/-   ##
==========================================
+ Coverage   96.98%   97.07%   +0.08%     
==========================================
  Files           1        1              
  Lines        1127     1127              
==========================================
+ Hits         1093     1094       +1     
+ Misses         34       33       -1

Impacted Files	Coverage Δ
cmd2.py	97.07% <0%> (+0.08%)	⬆️

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