Migrate all advisories to V2 format (closes #228)

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.

crates/security-framework/RUSTSEC-2017-0003.toml

@@ -1,7 +1,6 @@
 [advisory]
 id = "RUSTSEC-2017-0003"
 package = "security-framework"
-patched_versions = [">= 0.1.12"]
 date = "2017-03-15"
 keywords = ["mitm"]
 url = "https://github.com/sfackler/rust-security-framework/pull/27"
@@ -14,3 +13,6 @@ certificate.
 This issue was fixed by properly configuring the trust evaluation logic to
 perform that check.
 """
+
+[versions]
+patched = [">= 0.1.12"]