[mrattle]

Release v0.9.0

Fixes some broken tagging preventing rustdoc compilation, adds a related CI check.

PRs included in this release:
#91
#93
#94

[mrattle]

After merge:

❯ cargo publish
    Updating crates.io index
   Packaging async-memcached v0.9.0 (/Users/mark/src/github.com/Shopify/async-memcached)
    Updating crates.io index
    Packaged 44 files, 497.0KiB (89.0KiB compressed)
   Verifying async-memcached v0.9.0 (/Users/mark/src/github.com/Shopify/async-memcached)
   Compiling async-memcached v0.9.0 (/Users/mark/src/github.com/Shopify/async-memcached/target/package/async-memcached-0.9.0)
    Finished [`dev` profile [unoptimized + debuginfo]](https://doc.rust-lang.org/cargo/reference/profiles.html#default-profiles) target(s) in 0.69s
   Uploading async-memcached v0.9.0 (/Users/mark/src/github.com/Shopify/async-memcached)
    Uploaded async-memcached v0.9.0 to registry `crates-io`
note: waiting for async-memcached v0.9.0 to be available at registry `crates-io`
help: you may press ctrl-c to skip waiting; the crate should be available shortly
   Published async-memcached v0.9.0 at registry `crates-io`