Adlfs

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- Fixed bug in fetch_range that caused attempted reads beyond end of file
- Added check to mkdir when creating a container to confirm container_name conforms
to Azure requirements

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- Compatability with fsspec 2021.6.0
- `exists()` calls now also checks whether a directory with that name exists or not. Previously this was only checked from the cache
- Fixed bug in `find` not returning exact matches
- Added `AzureDatalakeFileSystem.rm_file` and `AzureDatalakeFileSystem.rmdir`
- Fixed bug in `filter_blobs` when target path contained a special character

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- Added the location_mode parameter to AzureBlobFileSystem object, and set default to "primary" to enable Access Control Lists and RA-GRS access. Valid values are "primary" and "secondary"

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- Now can create / destroy containers with `mkdir()`/`rmdir()` without needing to
have the privilige of listing all containers.
- When called with only container name, `exists()` now returns the proper result
(about the existence of the container) instead of a hard-coded `True`
- Removed version constraints on azure-storage-blob, pytest, and docker
- Updated conftest script to start Azurite docker container

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- fsspec version updated to 0.9.0

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- Updated path structure, so virtual folders in Azure blobs are created with a
trailing "/", to fix 137
- Converted all references to blob_clients to occur inside a context manager
- Added metadata to blob reads and writes, with {"is_directory": "<true or false>"}
to help resolve ambiguous folder and file discrepancies
- Minor update to assure compatibility with fsspec==0.8.7
- Added error handling to AzureBlobFile finalizer
- Updated AzureBlobFile.close method to execute threadsafe with asyncio
- Added check for leading "?" in sas_token parameter
- Fix for setting loop attribute on newer version of fsspec [197](https://github.com/dask/adlfs/issues/197)
- Converted self.mkdir() to a no-op to align to fsspec issue [562](https://github.com/intake/filesystem_spec/issues/562)
- Fixed errors with pyarrow write_dataset method related to pseudo-directories in [*171](https://github.com/dask/adlfs/issues/171).
- Fixed race conditions with finalizer on AzureBlobFile object
- Pinned fsspec to 0.8.7 to respect this change in async