Deserialize Cargo.toml

This is a definition of fields in Cargo.toml files for serde. It allows reading of Cargo.toml data, and serializing it using TOML or other formats. It's used by the lib.rs site to extract information about crates.

To get started, see Manifest::from_slice.

Additionally, this crate supports basic post-processing of the data to emulate Cargo's autobins feature, which sets manifest defaults based on presence of files on disk (other non-disk data sources are also supported).