Make Checklists Account for Custom Checklist Markers

[pjkaufman]

Fixes #748

Changes Made:

• Removed an unnecessary and incorrect comment
• Consolidated a lot of the checklist regex to be built on plugin load
  • This helps with performance so we are not building regex values more than 1 time when the value will be the same over and over again
  • This also allows for some uniformity on how checklists are found and matched as you can use a template and just have it reuse the value for the checklist box
• Broke apart and added a couple of examples to show that things were working
• Went ahead and fixed the wording on a couple of tests that I noticed was wrong
• Replaced old regex uses for checklists with the new regex that is built on load