Supports "dollar-slashy" string syntax introduced in Groovy 1.8.

The "dollar-slashy" string syntax is documented [here](http://beta.groovy-lang.org/docs/groovy-2.3.0-beta-2/html/documentation/core-syntax.html#_dollar_slashy_string).

I also made some fixes for compatibility with latest version of Prism, specifically:
- use `>` rather than `&gt;` when matching operators
- disambiguate annotations e.g. `@Canonical` from field access operator `.@foo`
- match `.` more carefully as punctuation and operator rules seem to be applied in a different order now

Example page with Jasmine tests is [here](http://freeside.co/prism-groovy/)