This is a big shift in the formatter API's. It simplifies the
responsibilities of the implementers so that pretty much all they
have to do it implement an iterator. Everything else will be
automatically derived from that. (Or, at least, that's the hope.)
This commit pulls the formatter out of the text buffer and
puts it in the editor instead. However, there is a lot of
commented code utlizing the buffer and formatter that still
needs to be updated.
In short, the editor is pretty non-functional in this commit.
File loading is now the responsibility of the Buffer, which allows
it to do some weird internal stuff to make it faster.
Also, using custom code for scanning the text, so all line endings
are handled now, not just LF and CRLF.
A LineFormatter determines how a line of text is visually displayed in
2d space. This allows both the Console and GUI version of the editor
to share the same buffer code whilst still handling the differing ways
in which both handle visual display.
There is now a CursorSet type that handles multiple cursors, and makes
it convenient to maintain the necessary invariants expected by the rest
of the code for multi-cursor editing.
