docs(manifest): Update crate-types with `cdylib`

docs(manifest): Update crate-types with `cdylib`

Rust 1.11 now supports the `cdylib` crate-type, so added it to the
list of options. Also added a link to the
[Linkage](https://doc.rust-lang.org/reference.html#linkage) section
in the Rust Reference manual which explains what the different
crate types actually mean in practice....though right now it actually
doesn't explain what a `cdylib` is, specifically. ;)