cargo: point `repository` metadata to clonable URLs

[lucab]

This tweaks the repository fields in Cargo metadata in order to use the correct (i.e. git clonable) URL. The existing GitHub webUI URLs for each package have been retained and moved to homepage fields.

[lucab]

For reference, without this PR the remote fetch would fail with:

$ git clone https://github.com/rust-lang/regex/tree/master/regex-automata

Cloning into 'regex-automata'...
fatal: repository 'https://github.com/rust-lang/regex/tree/master/regex-automata/' not found