3.0 notes and updates (#52)

* Add note on grid interactivity

* Ensure integers are integers in the examples

* Consistify use of TileJSON and consistify fillzoom json example with the spec description

* Ensure tile endpoints are absolute urls

* Use set of tiles instead of tileset

* keys and values

* update section order & put required first

* add extra note about bounds of one dimension

* define implementation

* add caching, schema.json

* add osm.json example

* add examples link

* fix link