Morecantile

* only import rasterio if needed (https://github.com/developmentseed/morecantile/pull/66)

* add `.rasterio_crs` properties to TMS for compatibility with rasterio (https://github.com/developmentseed/morecantile/pull/58)
* Use new Class-like notation for namedtuple (https://github.com/developmentseed/morecantile/pull/58)

**breaking changes**

* switch from rasterio to PyProj for CRS definition and projection transformation (https://github.com/developmentseed/morecantile/pull/58)
* remove python 3.6 supports (because of pyproj)

* add **NZTM2000Quad** tile matrix set from LINZ (author blacha, https://github.com/developmentseed/morecantile/pull/57)
* add **quadkey** supports (author adrian-knauer, https://github.com/developmentseed/morecantile/pull/56)

python
import morecantile

tms = morecantile.tms.get("WebMercatorQuad")

Tile to Quadkey
tms.quadkey(486, 332, 10)
>>> "0313102310"

Quadkey to Tile
tms.quadkey_to_tile("0313102310")
>>> Tile(486, 332, 10)


* update `NZTM2000*` CRS uri from `https://www.opengis.net/def/crs/EPSG/0/2193` to `urn:ogc:def:crs:EPSG:2193` (https://github.com/developmentseed/morecantile/pull/61)

* fix wrong TMS boundingBox definition when using inverted CRS (https://github.com/developmentseed/morecantile/pull/53)

* remove `mercantile` dependency.
* raise `PointOutsideTMSBounds` warning when user is doing operations outside TMS bounds.
* fix wrong `xy_bbox` when `tms.boundingBox` use a specific CRS.