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/yaml-rust/RUSTSEC-2018-0006.toml

@@ -3,6 +3,8 @@ id = "RUSTSEC-2018-0006"
 package = "yaml-rust"
 date = "2018-09-17"
 title = "Uncontrolled recursion leads to abort in deserialization"
+url = "https://github.com/chyh1990/yaml-rust/pull/109"
+keywords = ["crash"]
 description = """
 Affected versions of this crate did not prevent deep recursion while
 deserializing data structures.
@@ -12,6 +14,6 @@ that causes an abort while deserializing it.
 
 The flaw was corrected by checking the recursion depth.
 """
-patched_versions = [">= 0.4.1"]
-url = "https://github.com/chyh1990/yaml-rust/pull/109"
-keywords = ["crash"]
+
+[versions]
+patched = [">= 0.4.1"]