Updated version of the stats API

Would be good to make the stats API more efficient to better support the upcoming Looker Studio connector

We have made significant improvements to the Stats API: a way to retrieve your stats programmatically. The new V2 offers simpler querying, more flexibility with custom metrics, filters, and time ranges, and better performance when handling complex queries and large datasets.

Quick overview of the new capabilities:

• The new API supports breakdowns by multiple dimensions (previously named properties) and time ranges.
• Interactive documentation and playground which allows testing out queries in the documentation itself.
• New dimensions visit:country_name, visit:region_name and visit:city_name which simplify analyzing user behavior by location.
• New API supports custom ordering of results.
• Improved filtering: New structure requires less work from users to escape things.
• Improved filtering: New regular expression matching operator.
• Improved filtering: Complex conditions using OR/AND/NOT conditions.
• Increased limits for users on how much data is returned by a request for ease-of-use.