`{@inject}` is used for injected parameters instead of normal
parameters. It behaves the same as `{@param}`.

To forbid using the comment strings from their inner modes

Closes #4562

Closes #4468

Add template/variable definitions, checking, types, additional
keywords and indentation fixes.

Closes #3177

Also turn off reindentation inside strings and comments.

Issue #2980

See https://developers.google.com/closure/templates/ for documentation.
Closure Templates support text, HTML, JS and CSS code.

I'm not extremely happy with the indentation which is currently based
just on the Soy tags, not on the underlying code. Although this style
is possible and sometimes used, it's not the most common style.