Allow delimiters to be multi-character (longer words)

[colbert....@gmail.com]

I would like to use StringTemplate with a variety of computer languages, including declarative languages like xml, json, yaml, and sometimes hybrid-langauges like JavaScript and HTML.

The current version of StringTemplate supports only single-character delimiters (see delimiters instruction). In order to be used with multiple languages, StringTemplate should support defining delimiters that are longer than one character (like it's done currently).
>>> delimiters "%", "%"

We should be able to declare multi-character delimiters like

>>> delimiters "____DELIMITER_START", "____DELIMITER_END"