Upgrade mailto: to allow %HH escaping based on UTF-8
Advantages:
- Works very well with IRIs
- Works very well with UTF-8-based internationalized email addresses
- Straightforward for headers (e.g. ?Subject=...)
- Can work with ACE-based email address internationalization
- Makes Unicode -> ACE conversion part of the scheme-specific
interpretation rather than the generic IRI=>URI conversion
- Similar e.g. to IMAP
URIs (RFC 2192), which use %HH-escaped UTF-8, even if the IMAP
protocol uses modified UTF-7
- Works well in origin cases (MUA has to convert from Unicode to ACE
anyway for user interface)
- May work less well in 'proxy' cases (IRI/URI sent to third
party)
