Template conditionals/repetition

[nblumhardt]

Resolves #23

• Template tokenizer; since the template grammar is now recursive, we need a proper parser to handle it, and a tokenizer to feed it
• New template parser
• {#if ...} {#else if ...} {#else} {#end} conditions
• {#each ... in ...} {#separator} {#else} {#end} repetition
• Finish eliminating statically cached parsers to reduce working set, add user-constructable parser types for cases where many expressions/templates need to be parsed during a single application run - leaving this for now
• Update documentation

[nblumhardt]

You can see how the added syntax works:

• In the README
• In this example
• In this example
• And in the added evaluation tests

I'd love to spend some time widening test coverage, but I think quite a lot of the breadth of it is being exercised through the integration tests.

[nblumhardt]

Hmm no idea why CI isn't picking this up, will investigate.