Rio-tiler

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- add `preview` method to `rio_tiler.io.cogeo`

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- allow reading high resolution part of a raster (by making height, width args optional)
- add `max_size` option in `rio_tiler.reader.part` to set a maximum output size when height and width are not set
- add point and area function in rio_tiler.io.cogeo
- fix width-height height-widht bug in `rio_tiler.reader.part`

**depreciation**
- deprecated `out_window` option in favor of `window` in rio_tiler.reader._read

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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.