Rio-tiler

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- fix unwanted breacking change with `img_profiles.get` not allowing default values

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- make `rio_tiler.io.landsat8.tile` return Uint16 data and not float32 (173)
- `rio_tiler.profiles.img_profiles` item access return `copy` of the items (177)
- better colormap docs (176, author kylebarron)

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- add `rio_tiler.io.cogeo.info` to retrieve simple file metadata (no image statistics)
- add band metadata tag info in `rio_tiler.render.metadata` output
- add `rio_tiler.io.stac` STAC compliant rio_tiler.colormap.apply_discrete_cmap

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- only use `transform_bounds` when needed in rio_tiler.reader.part

Breaking Changes:
- switch back to gdal/rasterio calculate_default_transform (164). Thanks to Terracotta core developper dionhaefner.
- refactor `rio_tiler.utils.get_vrt_transform` to get width and height input.

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- Fall back to gdal/rasterio calculate_default_transform for dateline separation crossing dataset (ref 164)

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- added `reader.preview`, `reader.point` methods
- added multi_* functions to rio_tiler.reader to support multiple assets addresses
- added `rio_tiler.utils.has_mask_band` function
- added `rio_tiler.utils.get_overview_level` to calculate the overview level needed for partial reading.
- added type hints
- added scale, offsets, colormap, datatype and colorinterp in reader.metadata output (158)
- new `rio_tiler.colormap` submodule
- added `unscale` options to rio_tiler.reader._read function apply internal scale/offset (157)

Breaking Changes:
- removed python 2 support
- new package architecture (.io submodule)
- introduced new rio_tiler.reader functions (part, preview, metadata...)
- renamed rio_tiler.main to rio_tiler.io.cogeo
- bucket and prefixes are defined in rio_tiler.io.dataset.`{dataset}_parse` function from
AWS supported Public Dataset
- renamed `minimum_tile_cover` to `minimum_overlap`
- renamed `tile_edge_padding` to `padding`
- padding is set to 0 by default.
- use terracotta calculate_default_transform (see https://github.com/cogeotiff/rio-tiler/issues/56#issuecomment-442484999)
- colormaps are now have an alpha value
- `rio_tiler.utils.get_colormap` replaced by `rio_tiler.colormap.get_colormap`
- new `rio_tiler.colormap.get_colormap` supports only GDAL like colormap
- replaced `rio_tiler.utils.array_to_image` by `rio_tiler.utils.render`
- replaced `rio_tiler.utils.apply_cmap` by `rio_tiler.colormap.apply_cmap`
- replaced `rio_tiler.utils._apply_discrete_colormap` by `rio_tiler.colormap.apply_discrete_cmap`
- removed `histogram_bins` and `histogram_range` in options in metadata reader.
Should now be passed in `hist_options` (e.g: hist_options={bins=10, range=(0, 10)})
- remove alpha band value from output data array in tile/preview/metadata 127