v3.6.3: Likely final release of v3

This release integrates a few important bug fixes (thanks @vermiculus, @unkcpz) that have come in since the release of v3.6.2, and is the last release expected for the v3 series. The release of v4 is expected in about a month, and it will bring significant changes:

• the cross-platform API will become its own crate: keyring-core.
• each credential store will become its own store.
• this crate will become an example of how to write a keyring-based application.

PLEASE NOTE: with this release, the main branch has changed significantly. What was on the main branch has moved to be a v4 branch, and the main branch was reverted to v3.6.2 and then had bug fix commits added on. If you have an existing fork of this repository, you should immediately sync your repo by choosing the "discard commits" option, which will take your repo back to v3.6.2 and then pull the newer commits. Then, if you have development work on one of your other branches, you should rebase that work onto the updated main.