Release a version 0.6.1 of harfbuzz and consolidate Cargo configuration

[mrobinson]

I managed to publish this crate without checking out the git submodules
first, which breaks the bundled build. This version bump will ensure
that the latest version on crates.io can build.

[waywardmonkeys]

There's no need to bump the version for harfbuzz-traits ... Part of the point of that crate is that the version needn't change as often.

cc: @Manishearth @sffc

[mrobinson]

Some projects seems to use workspace versioning, which I think can make things a lot easier to understand for people using these crates. Here's an example: https://github.com/emilk/egui/blob/master/Cargo.toml#L23 As a person who has to upgrade a lot of dependencies, I find this easier to deal with. It's always clear what the latest version of the crate is.

[mrobinson]

I have updated this change to explicitly use workspace versioning, which should simplify new releases.

[waywardmonkeys]

That is worse.

harfbuzz-traits is meant to not change version except when absolutely necessary (a trait is added / removed / changed). That's why it exists rather than just having people use harfbuzz or harfbuzz-sys to get those traits.

[Manishearth]

I think this shouldn't inherit, yes?

[Manishearth]

Yeah I'm not sure if we should use workspace versioning. Everything else, yes.