Add a default set of "alternate" template delimiters

There needs to be an easy way for someone to handle `{%` and `%}` delimiters easily. It's too complex right now.

The issue names no files, tests, or entry points. Start by locating Grunt's template delimiter handling and clarify which default alternate delimiters and configuration behavior are required. Done should mean that `{%` and `%}` can be used through a documented, easy-to-configure default without the current complexity.

Written by the indexing model from the issue text.