Added getTemplateSettings and setInterpolationSymbols

While possible to change interpolation symbols {{ and }} by changing template options, it is error-prone.
setInterpolationSymbols changes template settings to use different interpolation settings.
E.g. dot.setInterpolationSymbols('<%', '%>') produces these options:
```
{
    evaluate: /\<\%([\s\S]+?(\}?)+)\%\>/g,
    interpolate: /\<\%=([\s\S]+?)\%\>/g,
    encode: /\<\%!([\s\S]+?)\%\>/g
    // ...
}
```