Bdbag

* Set "User-Agent" header for HTTP fetch handler (via `python-requests`) to `"bdbag/{version} (requests/{version})"`.
* Added `sha1` support for `bdbag_utils` function `create-rfm-from-url-list`. See PR [46](https://github.com/fair-research/bdbag/pull/46).
* Fix issues with unicode handling in `fetch.txt`, RO `metadata.json`, `keychain.json`, and `remote-file-manifest` JSON files.
* Fix issues with over-escaping (urlencoding) of filenames and urls in `fetch.txt` and RO `metadata.json`.
Per the spec, *only* CR,LF, whitespace, and literal percent should be encoded.

* [41](https://github.com/fair-research/bdbag/issues/41): Add support for regex patterns in `filter_dict`.
See PR [42](https://github.com/fair-research/bdbag/pull/42).
* Add `-frozen` qualifier suffix (when applicable) to version strings returned by get_distribution.
* Pinned `setuptools_scm<6.0` due to it dropping support for Python 2.7/3.5 which we will still support for a little while longer.

* Implement [37](https://github.com/fair-research/bdbag/issues/37): Support external fetch transports via plug-in
architecture.
* Added `--output-path` CLI (and corresponding API) argument for specifying output path for extracted archives.
* Added a `bypass_ssl_cert_verification` configuration option for the `https` fetch handler so that SSL certificate verification could be disabled
either globally (not recommended) or on a whitelisted set of URL paths used in simple substring matches against
a bag's `fetch.txt` URLs.
* Update the `--validate-profile` CLI argument so that it can take an optional keyword argument, `bag-only`, which
can be used to bypass the otherwise automatic profile serialization validation, and therefore is suitable to use
on extracted bag directories.
* Fixed issue with `archive_bag` API function not including empty directories when creating `zip` format archives.
* Modified `extract_bag` API function to accurately include the bag root directory path of the extracted bag
archive in the return value. Previously, this value could have wound up being different from the file archive base
name; for example if the archive file was renamed or was created in such a way that the base file name never matched
the archived bag directory root.
* Refactored `bagit-profile` support. This module is no longer "vendored" internally and is now a proper external
dependency intended to be pulled from PyPi. The `Profile` class is patched internally, as needed. This dependency
is currently pinned to `1.3.1`.
* Updated `bdbag-profile.json` and `bdbag-ro-profile.json` to leverage newer features of `bagit-profile` version
`1.3`. Loosened "Manifests-Required" to only require `md5` for both profiles.
* Pinned `bagit-python` dependency version to `1.8.1`.
* Added Python 3.8 and 3.9 support to `setup.py` metadata and travis builds.
* Dropped Python 3.4 support.

* Fix [34](https://github.com/fair-research/bdbag/issues/34): New file hashes for existing manifest entries generated
from remote-file-manifests don't get updated in bags.
* Fix [36](https://github.com/fair-research/bdbag/issues/36): Directory paths with a slash at the end during
"archive_bag" result in a malformed archive name.
* Added `update_keychain` API function in `auth/keychain.py` for add/update/delete of keychain entries.
* Added Python 3.7 support to `setup.py` metadata and travis builds.

* Ensure tag file manifest entries for additional tag files uses
denormalized path separator (unix-style `/`) similar to payload file
manifest entries.
* Return result bag path from the `materialize()` function.
* Don't use strict mode when guessing mime types to allow for user-extended types.
* Dropped Python 3.3 support.

* Fix 31: Missing import of `ensure_valid_output_path` in `fetch_globus.py`.
* Fix e745f98: Undefined `false` in `bdbag_ro.py` .