Omniduct

This is a minor release adding several new features.

New Features:
- Support for pruning the cache by specifying the target number of cached items.
- A more flexible configuration parser that is backward compatible with configurations from previous versions but relaxes the requirement that all duct configurations are equally nested (in response to 97).

Minor improvements:
- Omniduct will no longer insert its version into the source string during presto queries, better allowing downstream users to use it for query policies / etc.

This is a minor release which fixes an invalid version constraint on the `interface-meta` dependency that prevents Anaconda environments from correctly parsing Omniduct's dependencies.

This is a minor release with the addition of a new database backend for Exasol (contributed by foxyblue in 99; thanks!).

This is a minor release which does not install `enum34` on Python 3.4+ where it is not necessary, and has caused some trouble with other packages.

It also has some documentation fixes from foxyblue (100 102). Thank you!

This is a minor release fixing a bug introduced in v1.1.4 for SSH clients preventing connections due to cyclic references in the `connect()` method of `SSHClient`.

This is a minor release with several significant improvements over v1.1.3 that do not break the API. Most of the changes revolve around improving the filesystem clients and their performance.

- Improve performance of all `Duct` instances by skipping connection checks for every operation, and instead only check if actions fail. This was achieved by replacing `self.connect()` patterns with a `requires_connection` decorator, which only lazily checks the connection.
- Expose a wrapper around all Omniduct `FileSystemClient` implementations for use with `pyarrow` as `_.pyarrow_fs`.
- Fix serialization of `pandas` dataframes when using filehandles.
- Improve the robustness of cached methods when the serializer fails to serialize (or deserialize) objects.
- `FileSystemFile` fixes and improvements:
- Fix a `seek` implementation bug whereby `whence` was not passed through to the internal buffer.
- Fix the spelling of the `writable` attribute: "writeable" -> "writable"
- Add a few extra methods to the API to match that offered by `io` file implementations.
- `S3Client` fixes and improvements:
- Fix enumerating root "directory".
- Add support for passing in a pre-configured boto3 session.
- Refactor class to allow for subclasses to override boto3 session generation.