Scout-apm

Added

- Support Python 3.9.
([PR 583](https://github.com/scoutapp/scout_apm_python/pull/583))

- Moved core agent on Linux to default to the musl version, rather than try
detect whether to use the musl or GNU libc version.
([PR 585](https://github.com/scoutapp/scout_apm_python/pull/585))

Fixed

- Added a cast to string of query parameters, to work around cases where
application code changes them to non-strings. Fixes a possible exception:
`AttributeError: 'int' object has no attribute 'encode'` in
`scout.core.web_requests`.

Added

- Changed default agent connection to use TCP rather than a unix socket. By
default the agent will be run on 127.0.0.1, port 6590. This should resolve
a number of connection issues. To continue using a socket connection,
[configure
`core_agent_socket_path`](https://docs.scoutapm.com/#python-configuration).
([Issue 553](https://github.com/scoutapp/scout_apm_python/issues/553))
- Tested with Django 3.1. No compatibility changes were required, but this is
the first release to be tagged as supporting it.

Fixed

- Fixed validation check on length of key.
([Issue 563](https://github.com/scoutapp/scout_apm_python/issues/563))
- Update Core Agent to version 1.3.0, fixing several bugs and opening the
ability to run with only a TCP socket.
([Issue 567](https://github.com/scoutapp/scout_apm_python/issues/567))

Fixed

- On Django, only track the current user ID if `request.user` was accessed by
application code. This stops a `Vary: Cookie` header being injected due to
session data access.
([Issue 544](https://github.com/scoutapp/scout_apm_python/issues/544))

Fixed

- Always convert `collect_remote_ip` to boolean.
([Issue 542](https://github.com/scoutapp/scout_apm_python/issues/542))