As proposed in #240 and tracked in #414, this PR translates all
advisories into the new "V3" advisory format, which is based on Markdown
with leading TOML front matter.
This format makes it easier to see rendered Markdown syntax
descriptions, whether rendered by an IDE or GitHub. This should help
with both crafting advisories initially as well as review, and ideally
encourages more lengthy descriptions.
Support for this format shipped in `cargo-audit` v0.12.0 on
May 6th, 2020.
As announced in #228, this commit migrates all advisories to the new V2
format, which splits version information into a separate section, and
now has a structure which corresponds to the internal code structure of
the `rustsec` crate.
This is a breaking change for users of `cargo-audit` < 0.9, and anyone
who has written a 3rd party advisory format parser.
