Move open brace to previous line.
Add explanatory comment for what this is doing.
Convert `continuation_data` to use `extract_bits`.
Remove spaces after symbols.
Derp, fix signs
Clarify empty statement.
Add namespace comment.
Added tests from a stress test @mlucy found that make sense.
Fix style niggles.
Be more like the NULL byte error in `check_str_validity`.
First draft of iterator.
Convert older code to use new iterator.
Begin work on an iterator based approach to the parsing.
Add iteration error tests.
Encode the remaining stress tests.
Make other stuff use `next_codepoint`.
Make sure standard bracketed iteration works.

This is a little awkward because `iteration_t` has no idea where the
end actually is until it sees it; a bit like `istream_iterator`, and
the solution is similar.  `is_done` is provided for Java-like
iteration and sanity checking.