Manifest formats and utilities.
There are three types of manifests Binstall may deal with:
- manifests that define how to fetch and install a package
([Cargo.toml's `[metadata.binstall]`][cargo_toml_binstall]);
- manifests that record which packages _are_ installed
([Cargo's `.crates.toml`][cargo_crates_v1] and
[Binstall's `.crates-v1.json`][binstall_crates_v1]);
- manifests that specify which packages _to_ install (currently none).