Improve control flow and region token matching

[mlorbetske]

• Allow variations on control flow and region token matches
• Make the support for tag based languages more obvious for these cases
  • Right now, a match for <? if (condition) ?> would have to indicate its if token as <? if (including the space between ? and if and omitting the required element close ?>
  • This can be accomplished by adding a specific tag provider that activates on <? (or, generically, an appropriate language open token), consumes whitespace, provides an activation flag to the normal if handler, and returns control to the main scan - this will require some design

[mlorbetske]

This will need to be another evaluator like CppStyleEvaluatorDefinition

[mlorbetske]

Lower priority because the "whole line" option can trim out the garbage

[mlorbetske]

This should just be an extra operation using the extensibility points that will be introduced in #59