[WIP] Add vector-tile encoding benchmark

[jakepruitt]

Adds executable vector-tile benchmark, ./build/Release/vtile-encode that takes a geojson datasourceand a z x y tile coordinate, and an optional iterations parameter. Currently, the test renders the geometry from the geojson onto a vector tile for iterations number of times, logging the amount of time it took.

Things I want to add:

• [ ] Support for other input file types
• [x] -o for output .mvt file
• [ ] Pyramiding
• [ ] -r for a directory of inputs
• [ ] Support FeatureCollections

cc/ @flippmoke @mapsam @springmeyer

[jakepruitt]

@flippmoke - is there anything in here that looks like a red flag for being compatible with the v2_spec branch?

[flippmoke]

The other additional options here would be nice to have, but aren't required currently. Merging with current configuration.