FIX/FEATURE: Wrong month when using :date #67

Hi Sebastian,

this PQ should fix the problem described in https://github.com/dalekjs/dalek/issues/67. 

I changed _parseDate() and _parseDateTime() to return the date / datetime in ISO 8601 format (http://www.w3.org/TR/NOTE-datetime). Please check the commits and the code and merge if satisfied.

Kind regards
Marc