Add ability to prettify HTML outputs

[dac514]

Debugging feature,

[codecov]

Codecov Report

Merging #1036 into dev will decrease coverage by 0.06%.
The diff coverage is 93.33%.

@@             Coverage Diff             @@
##               dev    #1036      +/-   ##
===========================================
- Coverage     49.8%   49.74%   -0.07%     
- Complexity    3395     3397       +2     
===========================================
  Files           87       87              
  Lines        14865    14874       +9     
===========================================
- Hits          7404     7399       -5     
- Misses        7461     7475      +14

[greatislander]

@connerbw I don't know if this is intentional but should we add the $tidy option to the HTMLBook beta as well?

[dac514]

It's intentional. We can't tidy XTHML by default because we don't want to introduce bugs (what do formatting and extra spaces do to existing outputs? Probably nothing but we can't know for sure.). My hope HTMLBook/HTML5 should be tidy from the start.