Use interpolationSymbols

Hi! Your module works great and is just what I was looking for, so thank you. 

This branch has a small change, but one that I ended up needing because I had overwritten angular's default interpolation symbols from `{{` to `{[`. I noticed that when the html for the `<link>` is generated the symbols were hardcoded so I injected `$interpolate` and used that to get the symbols from the app. That way it should handle things whether or not the symbols were changed.