mailto: scheme stays exactly as currently defined, allows only US-ASCII,
no escapes
Advantages:
- Works will with ACE-based email addresses
Disadvantages:
- Does not work well with IRIs (can use US-ASCII only in IRIs, but this
defies the purpose of IRIs)
- Does not work well with UTF-8 internationalized email addresses
- can work to some extent; reverse issues from ACE-based issues on
last slide
- Would need additional work for headers (e.g. ?Subject=...)
