Rio-tiler

------------------
- fix nodata (48)

------------------
- 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

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

------------------
- Support for additional CBERS instruments (fredliporace)

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

------------------
- adds DatasetReader input option for utils.tile_read (do not close the dataset on each read)

Breaking Changes:
- `utils.tile_band_worker` renamed to `utils.tile_read`
- `main.tile` **rgb** option renamed **indexes**
- `sentinel2.tile`, `landsat8.tile`, `cbers.tile` **rgb** option renamed **bands**
- `main.tile` default nodata mask is handled by rasterio