Rio-tiler

* Added [pystac.MediaType.COG](https://github.com/stac-utils/pystac/blob/master/pystac/media_type.py#L4) in supported types by STAC reader
* fix bad type definition in `rio_tiler.colormap.ColorMaps` data (https://github.com/cogeotiff/rio-tiler/issues/359)
* add `rio_tiler.colormap.parse_color` function to parse HEX color (https://github.com/cogeotiff/rio-tiler/issues/361)

* Reduce the number of `.read()` calls for dataset without nodata value (https://github.com/cogeotiff/rio-tiler/pull/355)
* replace deprecated `numpy.float` by `numpy.float64`

* fix bad mask datatype returned by mosaic methods (https://github.com/cogeotiff/rio-tiler/pull/353)
* align WarpedVRT with internal blocks when needed. This is to reduce the number of GET requests need for VSI files (https://github.com/cogeotiff/rio-tiler/pull/345)

* fix arguments names conflicts between mosaic_reader/tasks and STACReader options (https://github.com/cogeotiff/rio-tiler/pull/343)
* update rio-tiler pypi description.

* add MultiPolygon support in `rio_tiler.utils.create_cutline` (https://github.com/cogeotiff/rio-tiler/issues/323)
* support discrete colormap by default in `apply_cmap` (https://github.com/cogeotiff/rio-tiler/issues/321)
* delete deprecated `rio_tiler.mercator` submodule
* added default factory in `rio_tiler.colormap.ColorMaps`.
* fix missing `metadata` forwarding in `ImageData.post_process` method.
* refactor `rio_tiler.io.GCPCOGReader` for better inheritance from COGReader.

**breaking change**

* renamed input parameter `tile` to `data` in `rio_tiler.utils.render`.
* renamed input parameter `arr` to `data` in `rio_tiler.utils.mapzen_elevation_rgb`
* made `rio_tiler.io.stac.to_pystac_item` private (renamed to `_to_pystac_item`)
* renamed `rio_tiler.colormap.DEFAULTS_CMAPS` to `rio_tiler.colormap.DEFAULT_CMAPS_FILES`
* made `rio_tiler.reader._read` public (renamed to rio_tiler.reader.read) (ref: https://github.com/cogeotiff/rio-tiler/issues/332)

* add `NPZ` output format (https://github.com/cogeotiff/rio-tiler/issues/308)
* add [pystac](https://pystac.readthedocs.io/en/latest/) for STAC item reader (author emmanuelmathot, https://github.com/cogeotiff/rio-tiler/issues/212)
* delete deprecated function: `rio_tiler.reader.tile`, `rio_tiler.utils.tile_exits` and `rio_tiler.utils.geotiff_options`
* deprecated `rio_tiler.mercator` submodule (https://github.com/cogeotiff/rio-tiler/issues/315)
* update morecantile version to 2.1, which has better `tms.zoom_for_res` definition.