Replace doT templates with tempura or another templating engine

[MikeRalphson]

doT is/was maintained by the author of ajv, but ajv no longer uses doT and I suspect it will not get much maintenance going forward.

I have looked at tempura from @lukeed which is actively maintained (though new) and appears to be faster than doT (though that may not be a major consideration for most widdershins users).

The syntax is very similar to handlebars or mustache, but with simple logic flow helpers.

My initial thought is to support but deprecate doT templates in the next major version of widdershins, and either try to parse templates as tempura but fallback to doT if compilation fails, or have an option to control the template engine. In the next major version after that, support for doT templates would be removed.

Any and all thoughts gratefully received. Thank you.

[lukeed]

Oh hey, thanks! Lemme know if you need anything.

A few people have found the strictness of tempura templates to be an obstacle. I definitely prefer the strictness (aka, need to #expect the var names the template will be using), but it does make the transition from handlebars/wherever slightly more difficult. So I'm releasing a new version that now supports options.loose.