[CM] pattern updates and fixes

[Rick Taube]

Ive  completely rewritten cm's pattern documentation and added new 
(hopefully more useful) examples of usage in the dictionary. the 
dictionary also contains a new "overview" page that will (hopefully) 
help newcomers understand how to use them. the new tutorial page is 
here:
	http://pinhead.music.uiuc.edu/~hkt/cm/doc/dict/patterns-topic.html
and it has links to all the new/updated pattern docs. please let me 
know of any errors or bugs!

ive also fixed a few bugs/misfeatues in patterns.scm and in output to 
midi files in the last few days (thank you anders!) see the changelog 
for an explanation