fix symbolic links plus general cleanup

Symbolic links were partly broken:

• cross-scheme links would sometimes fail, e.g. if there was a matching name in the filesystem (could not link /dev/tty to libc:tty)
• relative links appear to be relative to the original url, which will not be true for multiple hops
• canonicalize was written in u8 instead of utf8, for no good reason

This MR fixes the above, and enables /dev/tty to be linked to libc:tty.

Some additional cleanup of warnings and format was done