Rio-tiler

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- allow setting default kwargs in COGReader __init__ (227)
- allow `vrt_options` in COGReader.point
- add `rio_tiler.io.base.MultiBaseReader` class (225)
- refactor `rio_tiler.io.stac.STACReader` to use MultiBaseReader (225)
- add `rio_tiler.task` submodule to share tools for handling rio-tiler's future tasks.
- fix regex parsing for rio-tiler expression
- add warnings when assets/indexes is passed with expression option (233)

Breaking Changes:
- replace dataclass wiht attr to support more flexible class definition (see 225)

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- add `utils.create_cutline` helper (218)
- remove any mutable default argument

**depreciation**
- `warp_vrt_option` is replaced by `vrt_options` in rio_tiler.reader.part (221)

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- add more verbosity to mosaic error (214)

Breaking Changes:
- `rio_tiler.mosaic.reader.mosaic_reader` return `((tile, mask), assets_used)`
- `COGReader.info` is now a method instead of a property to align with other reader (211)

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- add rio_tiler.io.base.BaseReader abstract class for COGReader and STACReader to inherit from
- STACReader raises `InvalidAssetName` for invalid asset name or `MissingAssets` when no assets is passed (208)
- update rio_tiler.mosaic.reader.mosaic_reader to not use threadPool if threads <= 1 (207)

Breaking Changes:
- Reader.spatial_info is a property (203)
- assets is a keyword argument in STACReader stats/info/metadata

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- add `rio_tiler.mosaic` submodule (ref: https://github.com/cogeotiff/rio-tiler-mosaic/issues/16)

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- add boto3 in the dependency (201)