use workspace inheritance for common version

[dead10ck]

By using the top-level Cargo.toml and workspace inheritance, we can eliminate all the duplication of the version number, and make cargo build report the correct version (rather than the old 0.6.0). This does require adding a patch version to make it semver compatible.

[pascalkuthe]

I would like to see the same thing being done for dependencies too (both so we get a better overview of all external dependencies and avoid duplicate versions) but that can be a separate PR

[the-mikedavis]

Could you also update the release docs to mention that the version should be bumped in ./Cargo.toml now rather than ./VERSION?

helix/docs/releases.md

Lines 12 to 13 in b7f98d1

	* Edit the `VERSION` file and change the date to the next planned release
	* Releases are planned to happen every two months, so `22.05` would change to `22.07`

The sub-bullet there could also probably use a bit of rewording, something like: "Releases are planned to happen every few months as time allows. Versions follow CalVer so a release in May of 2022 would be 22.05.0" (Since we'd like to experiment with smaller releases around 1mo and sometimes end up with larger releases more than 3mo.)

[dead10ck]

Ok this was changed to still use the Cargo.toml, but it drops the micro version if it's equal to 0. This will let us track the project version with Cargo, while the user facing version format remains unchanged.