Refactor api

Here are some of my ideas around refactoring how InfluxDB's API works. The key learning here is that people have been using string columns like tags and it leads to bad performance.

My goal here is to make that the default and to expose an API that is more purpose built around the metrics/time series use case as opposed to the more general purpose SQL.

Please comment on the individual lines of [influx_api_v2.md](https://github.com/influxdb/influxdb/blob/refactor-api/influx_api_v2.md) for focused feedback. Or leave comments in the thread for more general thoughts.

I'm also very interested in hearing about specific use cases. Have I captured everything here? What have I left out? I know this can't encompass everything, but my hope is that it creates a clean foundation that we can easily expand upon.

@jvshahid, @toddboom, @benbjohnson, @dgnorton, @otoolep: please to review.
One problem i have with your approach, if the user is asking for all `cpu_load` data points, then we have to merge across all series. Keep in mind that this is multiplicative, meaning if you have 3 tags with cardinality of 10 then you have to merge 1K time series together. This example might sound little silly but keeping the cardinality fixed, the number of series to be merged will be O(C^t) where `C` is the constant cardinality and `t` is the number of tags, i.e. it's exponential in the number of tags.