Parse URLs fully (in cargo)

[graydon]

We should just have a URL library in std. It's a normal function these days.

[brson]

What does fully parsing urls in cargo entail? Where are we not doing so?

[graydon]

std::net_url is fine as far as the stdlib part goes; it's just that in cargo.rs we have some kinda ad-hoc string scanning (has_archive_extension, is_archive_url, is_git_url, assume_source_method) that should probably delegate to std::net_url.

[z0w0]

Closing because Cargo is obsolete as of version 0.6. Rustpkg makes use of both std::net_url for bare URLs and paths for custom sources (not sure what they're called yet).