DRAFT Roadmap Requests 3.0

[jrfnl]

This issue is intended to contain a tentative roadmap for things to be included/removed in Requests 3.0.

For now, the most important function of this issue is to contain an action list to keep track of follow-up actions from current PRs/issues, which need to be handled in a future major release.

Action list

• Remove support for the deprecation notice silencing about use of the PSR-0 classes.
  I.e. remove support for the REQUESTS_SILENCE_PSR0_DEPRECATIONS constant.
  Related: Requests 2.0.0: introduce namespaces #519
• Make more classes final. See More classes planned to be made final #866
• Drop support for PHP < 7.2.
• Replace input validation in methods with parameter type declarations wherever possible.
  Related: Add input validation #593 and Review parameter type declarations #873
• Add return type declarations wherever possible (non-union types).

[jrfnl]

Updated the roadmap to remove references to dropping PHP 7.1 in favour of 7.2 and removing the uncertainty about doing this. As WordPress (the biggest Requests user) has now dropped support for PHP < 7.2, I expect we should be able to drop support for PHP < 7.2 in Requests as well.