allow bypassing html_escaping

[mistercrunch]

In some cases mustache/chevron can be used to template strings that
are not html, for example templating SQL or other languages/strings like
markdown.

[coveralls]

Coverage remained the same at 100.0% when pulling ebdd476 on mistercrunch:no_escape into 78f1a38 on noahmorrison:master.

[dcmoore-gd]

Would the existing {{{ ... }}} syntax not be sufficient for those use cases?

[mistercrunch]

Oh. {{{ ... }}} is a great workaround for us that I wasn't aware off, though html-escaping in our context never makes any sense and not using it should be more the rule than the exception. I think that's true of all templating use-cases that are not targeting HTML.

[mistercrunch]

closes #79

[noahmorrison]

I'm going to reject this in favor of using the triple brackets, which is what the spec recommends.

I'm not horrendously opposed to implementing this, it just seems unnecessary. Maybe I'll add a non-html mode later on if there's more community desire for such a mode.