Support expressions in braces

[citizenmatt]

Should support expressions in attributes or element text wrapped in brackets - {{...}}

[ngbrown]

I think this is the same as issue #3.

[citizenmatt]

#3 is more about handling $scope inside expressions, and this issue is about enabling support for expressions in {{...}} blocks, in the same way that expressions are currently supported (e.g. syntax highlighting) for ng- attributes.