Support a qualified path in affected.functions

[Qwaz]

Continued from: #320 (comment)

Supporting a qualified path in affected.functions field would allow to describe the affected functions more precisely, especially when the bug is inside a trait implementation.

[tarcieri]

I relaxed the checks for the contents of this field quite a bit in rustsec crate v0.22, but this case is still disallowed.

I'm thinking in the next release we can remove pretty much all of the validity checks from this field and move them into the linting process so they're easy to change.

Note that we still won't be able to populate this field with anything that breaks the current rules until all clients have updated, however.

[pinkforest]

This works today now with latest rustsec:

RUSTSEC-0000-0000.md
functions = { "mycrate::MyType::<impl>Clone::clone" = ["< 1.2.0, >= 1.1.0"] }

$ rustsec-admin lint . --skip-namecheck rustdecimal|grep 0000
Linted ok: ./crates/mycrate/RUSTSEC-0000-0000.md

From code all I see now in checks is that the initial mycrate:: matches crate name mycrate

Closing as completed - We can re-open in rustsec/rustsec if further changes etc.