Support for absolute file paths in Windows

[tjtelan]

Example:

use git_url_parse::GitUrl;

fn main() {
  GitUrl::parse("C:\\test_repo");
}

thread 'main' panicked at 'index out of bounds: the len is 1 but the index is 1', src/lib.rs:237:39
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

It just doesn't work, but I am also testing in Linux and MacOS. I'm not sure if the Url crate handles this cross-platform.

This one will need a test that runs in CI. Probably in a Windows runner, if possible.