Fix auto execution of model commands

[Matthiee]

• Add extension method to verify parsing succeeded
• Added more xml comments
• Improved some tests
• Allow to disable auto execution on model commands

[codecov-io]

Codecov Report

Merging #38 into master will decrease coverage by 0.22%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master      #38      +/-   ##
==========================================
- Coverage      96%   95.78%   -0.23%     
==========================================
  Files          36       36              
  Lines        1127     1139      +12     
==========================================
+ Hits         1082     1091       +9     
- Misses         45       48       +3