v0.1.3 added shortcuts to simplify template language

@imlucas 
* Changed `Double` to `Number` to hide Javascript's `Number` constructor
* Added shortcuts `N, D, O, B` for `Number, Date, ObjectID, Boolean`
* Added shortcuts `f` for `faker` and `c` for `chance`
* Added `_$index`
* Made the former `_$size()` a property `_$size`