Backport new syntax to 3143

[Thom1729]

The new syntax fixes a number of bugs, but because it uses embed/escape it currently requires a Sublime dev build. There are several open issues that seem to indicate that many people are using the old syntax. In particular, the old Vue syntax has trouble with JavaScript syntaxes other than babel-sublime, including the core syntax (e.g. JS Custom).

Backporting the new syntax to 3143 would fix these bugs for these users. Doing so would require removing the uses of embed/escape, presumably replacing them with with_prototype.

[Thom1729]

This is pointless now that 3.1 is out.