Sort the reserved sigils, check for completeness

[aphillips]

In #574 I suggested that the sigils should be sorted in the ABNF. This is to track that comment.

currently we have:

reserved-annotation-start = "!" / "@" / "%" / "*" / "+"
                          / "<" / ">" / "?" / "~"

I would suggest this, which is in code point order:

reserved-annotation-start = "!" / "%" / "*" / "+"
                          / "<" / ">" / "?" / "@" / "~"

Also, are we missing these ASCII punctuation items: :, ;, (, ) ? (Note that & and ^ are private use sigils)

[eemeli]

We can't reserve : because we're using it for :functions, and ; is too close to it in appearance.

If we do want to consider (), then we should probably also consider []. But that's best done in a separate issue.

[aphillips]

Sorry, not : for sure. I don't think semi-colon would be wrong to reserve. We just probably never want to use it. I didn't put [/] because we had farted around with using those for keys... but that ship apparently has sailed. Since this is addressed by one of your PRs, we can make another issue for enclosing reserved characters (/) and [/].