Flip unless/else
#format_script: extract private method #preserve

* Inline ugly strip
#format_script: only check ugly once
#format_script: add locals for common setting combinations

* Add in_tag_no_nuke & preserved_no_nuke local booleans
* Inline if/elses
* Avoid possible undeclared local variable warnings
#format_script: use string interpolation instead of +
#format_script: add performance note

This causes a significant performance regression:

format_script(result, opts = {})