Adlfs

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- Added ability to connect with only connection_string.
- connection_string now pre-empts other credentials.

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- Added ability to fetch multiple AZURE_STORAGE_XYZ credentials as environmental variables

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- Removed weakref and added close method to fix memory leak
- Added **kwargs reference to _cp_file

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- Implemented asynchronous uploads and downloads of AzureBlobFile objects
- Aligned on policy for asynchronous context managers to be preferred with blob_client.
- Added abfs.makedir() method and aligned exist_ok parameter to fsspec api
- Updated abfs.mkdir() method to align to fsspec api.
- Pinned azure-storage-blob >= 12.5.0,<12.7.0 -- version 12.7.0 breaks compatability with azurite for unit testing

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- Fixed expception raised when commiting writes of large blobs
- Improved performance when checking for the existance of a key in a container with `.exists()`
- Improved performance of `.find()`
- Improved documentation for Azure SDK
- Fixed failed authentication when passing a credential

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- Updated azure-storage-blob dependency to >=v12
- Addede azure-core as dependency for exception handling
- Updated code for compatibility with fsspec > 0.6