A set of iterators which return the characters making up a "print positions", rather than the individual characters.
A print position is a potentially multi-byte slice of string which a user would read as a single 'character' on the screen or printed page. This print position contains a single UAX#29 extended grapheme cluster, possibly surrounded by ANSI escape codes. Escape sequences and control characters are assumed to not consume visible space.
This is handy for laying out text on an Ansi-compatible console screen, where ANSI SGR codes are used to set text colors and intensity and the text is non-ASCII unicode. You can count the returned graphemes as one column each and pad the rest of the field with blanks to the desired visual width.
Most ANSI sequences change the rendering of the characters that follow them, so they are
embedded at the beginning of the returned grapheme slice.
However, codes that reset special rendering modes, such as SGR reset and RIS,
are embedded at the end.
This allows caller to insert an undecorated string into the middle of a
decorated string (e.g, SGR something text SGR RESET) without having to track the rendering state, so long as the
insertion is done on print position boundaries.
But some ANSI sequences and control codes in fact do move the cursor or otherwise consume a print position and will be iterated out as part of some returned print position. This package does not attempt to track the screen cursor position, we blithely assume such sequences will not be input to the iterator. This is arguably a bug in the case of backspace, tab, newline, CUP and several more. PRs or simple suggestions for improvement are welcome!