Perceval

**Bug fixes:**

* [confluence] KeyError exception when arguments not passed to 'fetch_items'\
Required arguments that weren't passed to 'fetch_items' made the code
fail with a KeyError exception.

**New features:**

* [confluence] Option `max_contents` to limit the number of requested contents\
This parameter sets the maximum number of contents requested per
query. By default, this number is 200, but this can be changed by
adding the `--max-contents` argument. This will help to bypass those
instances where the maximum limit is lower than Perceval's default
value.

**Bug fixes:**

* [bugzillarest] Failback when checking custom instances\
Some Bugzilla instances return a HTTP 400 error when checking if their
are custom instances or not. On those cases, the backend will capture
the error and consider the version of that Bugzilla instance as
custom.
* Slack identifier extraction fixed\
Extract the identifier without user information when the user was
deleted.

**New features:**

* [bugzillarest] API Key authentication\
A new authentication is available in the `bugzillarest` backend using
an API Key. This can be provided using the parameter `--api-key` on
the command line. Note that this parameter will invalidate `--backend-
user` `--backend-password`, and `--api-token` parameters. For
developers, this parameter is also available during the initialization
of the class `BugzillaRESTClient` under the name `api_key`.
* Confluence supports fetch by spaces\
This allows fetching confluence by specific spaces. By default it will
fetch the entire instance, but adding the `--spaces` argument will
fetch only these spaces.

**Feature removals:**

* Drop Python 3.6 support\
Python 3.6 reached the end of life at the end of 2021. This means it
won't receive new updates or patches to fix security issues.
Therefore, this package will only work with Python >= 3.7 from now on.

**New features:**

* Add Rocket.Chat backend (543)\
Added support to fetch messages from a Rocket.Chat channel. The
messages are fetched in an ascending order based on time when they
were last updated. The channel information is also fetched. The tests
have been added accordingly. The usage docs have been updated.

** New features and improvements: **

* So far, the JSON items written to the defined output (standard output
by default) were difficult to parse. With the option `--json-line`, each
item will be written in one line, making easier their consumption by
other processes.
* New set of backends added:
- **GoogleHits**
- **Twitter**
* Minor bugs were fixed and test coverage was improved.

** Backend improvements: **

* **gitlab**
- add merge request category
* **github**
- increase the number of items retrieved per page
- add the list of commits hashed included in pull requests
* **mediawiki**
- optimize the number of API calls
* **pipermail**
- disable SSL verification

** New features improvements: **

* Problems with namespaces were fixed. This package was not really using
Python namespaces. When other packages, such as `perceval-mozilla` or
`perceval-opnfv`, were installed `__init__.py` (inside `perceval`)
were overwritten breaking the structure of the main package and making
Perceval unusable. This release defines `perceval` as a namespace. Due
to it, `fetch`, `find_backends` and other symbols are no longer accessible
from the main package.
* Mattermost backend added.