add tests for syntax errors
parser support for some handlebars-style syntax

{{#if ...}} {{/if}}
{{#unless ...}} {{/unless}}
{{#each ...}} {{/each}}
{{#with ...}} {{/with}}

Not supported: {{else}}

Also, {{#each x}} behaves much like {{#x}}, so you can do {{#each x:i}}

Closing tags are a lot more strict now. You can only use {{/opening}} or {{/()}} for expressions.

This breaks some conditions. Unsure if it's desirable (warning maybe?)