Support for different interpolation symbols

Heya,

I am writing an app with Symfony 2 and Angular, and because they both want to use `{{` and `}}` in their templating systems, in order to get them to coexist I had to change it to `{[{` and `}]}` with:

```js
var App = angular.module("app", [ "smartTable.table" ], function($interpolateProvider) {
  $interpolateProvider.startSymbol("{[{");
  $interpolateProvider.endSymbol("}]}");
});
```

This is all well and good, except that SmartTable has `{{` and `}}` hardcoded throughout.  Therefore I added `--startSymbol` and `--endSymbol` to the grunt build script which simply adds a task that runs through the code with a regexp.

Thanks for an awesome directive!

Dave Keen