Dealing with Invalid UTF-8

[jasnell]

The current header compression draft states that header field values are UTF-8. However, the spec says nothing about how to deal with overlong encodings, invalid UTF-8 octet sequences or valid UTF-8 sequences that encode invalid Unicode codepoints.

I recommend stating that any of these conditions ought to result in an error. An encoder MUST NOT output any of these; and a decoder ought to signal a connection error if encountered.

[martinthomson]

Decided on a plan for #242 that invalidates this issue. Closing.