Rio-tiler

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- add schwarzwald color palette

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- fix nodata (48)

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- adapt to rasterio 1.0b4
- fix mask (internal/external) fetching 🙏
- fix boundless read with new rasterio 1.0b2
- fix custom nodata handling
- fix performances issue

Breaking Changes:
- removed alpha band options to select a custom alpha band number

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- Fix rasterio version to 1.0b1 (46 and 44)

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- Support for additional CBERS instruments (fredliporace)

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- Fixes sentinel-2 band 8A regex bug in `rio_tiler.utils.expression`