Policyd-rate-limit

Add
---

* Add the possibility to store limits_by_id in a mysql or pgsql database
* Add a new count mode (2) to count submitted emails and not recipients

Changed
-------

* Switch from MySQL-python to mysqlclient, a maintained fork in the README

Fixed
-----

* Only purge report table if it exists.

Fixed
-----

* Use Loader=SafeLoader for each yaml.load() call
* Mail not sent but decuted from quota (change the way recipients are counted.)

Changed
-------

* Switch from Travis CI to Github Actions

Bugfixes
--------

1. Handles properly the closing of connections by the MTA
2. Fix an error raised by an undeclared variable
3. Clears read sockets after processing, otherwise the reuse of the
sockets makes the accounting totally wrong (Closes: 13)

Fixed
-----

* typos
* Add 1 missing char to the rapport table width
* Disable pip cache then installing with make install
* Fix a db deadlock when running the script with --cleanup
* In case of error during a read from postfix, display the whole traceback
* Handles socket reuse by postfix
This was causing delay in mail delivery as postfix had to detect the
connection was closed. This was taking about 1s by recipient in a mail
and could dramatically slow mail delivery.


Added
-----

* Add possibility to limit by sender e-mail address as requested in
* Allow to send reports to multiple email addresses.

Fixed
- Tests on global install:
- Add default policyd-rate-limit.yaml to package data as it is used for
building the tests config file
- Only compute coverage if the coverage binary is found in the path as
it is optional and generally wont be available on a global install

Added
- Add possibility to overide limits by ids (id are sasl username or ip addresses)
- Add unit tests and CI

Fixed
- Deal with possible unavailable database backend. Return the value of `db_error_action`
instead of crashing.
- Only count in limit if the protocol states is RCTP.

If the policy delegation in postfix configuration is in smtpd_recipient_restrictions
as said in the doc, possible states are RCPT and VRFY.
- Fix random error "dictionary changed size during iteration" on exit