2008/04/06:

line numbers/margin support

2008/04/02:

fix read-only warnings to seem less junky (e.g. catch the buffer.ReadOnlyError
exception and write a graceful message everywhere applicable).

2008/03/18:

finish arg documentation and review method documentation

2008/03/16:

pdb/gdb/perldb buffer integration
error/stack-trace buffer

2007/10/20:

Tags for matching should be allowed to be multi-character, and should be
a list of data/type pairs (rather than several lists).

2007/08/11:

Instead of storing method state in the method objects (for mode callback stuff),
we should probably store it in the buffer.
AMENDED (2007/10/21): we should probably just store the entire mode in the
buffer, rather than storing all this junk piecemeal.

2007/07/19:

The minibuffer should be able to expand to become multi-line if the
prompt/input string becomes too long.

2007/07/17:

It would be nice to be able to toggle various lexing rules on/off, so that for
instance text mode could make spell checking optional, or optionally highlight
URLs/emails/etc.
AMENDED (2008/03/20): in the case of spell-checking and other non-standard
rules, we can do this with state variables in the mode. 

2007/07/15:

Vertical split would be awesome. Also, need more fine-grained controls for
even horizontally split windows.

2007/07/15:

Rename "lexing" to "parsing" since really we have moved way beyond a simple
lexing/tokenization strategy.