Omniduct

This is a minor release the introduces several improvements to the existing library.

Features and enhancements:
- Added two new serializers for use with the new cache API: BytesSerializer and PandasSerializer
- Added a `cache_namespace` attribute to all `Duct` instances, and use it (if provided) as the default cache namespace for the `cached_method` constructor.
- Added support for prepare-time lookup of cache filesystem from registry, and checks to ensure filesystem is connected before performing cache storage operations.

Bugfixes and cleanups:
- Fixed the default serializer in `cached_method` not being instantiated.
- Removed the (now unused) serialization code from CursorFormatters.

This is a minor release that includes one new feature to smooth the migration from v0.8.7 to v0.9.x.

`FilesystemCache` instances will now verify that the nominated cache directory is initially empty, and then persist a configuration file to mark the directory as initialised. This configuration will later be used to handle resource restrictions/etc. This should allow easier migration from older version of omniduct where existing cache files may clash with the structure used by the new cache structure.

This is a significant feature release with breaking changes to the API.

Breaking changes:
- `DatabaseClient.push` renamed to `DatabaseClient.dataframe_to_table` for increased consistency.
- The `local_cache` Duct has been removed, in favour of a new `filesystem_cache`, which is built on the new `Cache` API. It can run on arbitrary filesystems (local, remote, etc), and is much more flexible.

Features and enhancements:
- Database Clients:
- Support for session properties for database clients (with implementations for Presto, Hive and PySpark backends).
- Support for 'CREATE TABLE AS' statements via `DatabaseClient.query_to_table`.
- Support for dropping tables via `DatabaseClient.table_drop`.
- `DatabaseClient.push` renamed to `DatabaseClient.dataframe_to_table` for increased consistency.
- Filesystems:
- Support for removing files and directories via `FileSystemClient.remove`.
- '~' prefix is now recognised on all filesystems to refer to the "home" path.
- Cache:
- API significantly refactored to be more flexible and intuitive, with better documentation.
- `LocalCache` was replaced with `FilesystemCache`, which works atop any `FileSystemClient` backend.
- General:
- Support for disabling omniduct logging.

Behind the scenes:
- Added some new unit tests for database backends. Much more work to be done here.
- Streamlined some of the querying logic in `DatabaseClient`.
- Namespace parsing for table-specific methods in `DatabaseClient` for better runtime validation.

This is a minor release with one bugfix:
Stop iteration after exhausting contents of a file when proxied via FileSystemFile.

This is a minor release with one bugfix:
Fix typo that made indeterminate progress bars the default.

This is a minor point release with one improvement:
Allow use of dependencies which are not actually installed but simply available on the Python path.