the Tools menu will be for plug-in tools that can be written by
contributors. the scheme will be similar to the way libraries are
implemented, where everything in the "tools" subfolder of processing will
be added to the menu.

the full details of this need to be worked out so that others can begin
developing their own tools. lots of work also needs to be done with
determining a proper api for the use of this menu. obvious things are
access to the sketch object and to be able to modify text, but what other
sorts of hooks would be useful?

Added for 0147, with some initial help from fjen.