[Initial import.
Will M. Farr <farr@mit.edu>**20070815143202] 
[TAG 1.0
Will M. Farr <farr@mit.edu>**20070815143217] 
[Added deriv? predicate.
Will M. Farr <farr@mit.edu>**20070815162405] 
[Updated documentation to refer to version 2.
Will M. Farr <farr@mit.edu>**20070815162529] 
[Added contracts to exports.
Will M. Farr <farr@mit.edu>**20070815180633] 
[Fixed bug where inner derivatives could remove deriv structures associated with outer derivatives and extract-derivative would return an error instead of 0.  (Reported by Barak A. Pearlmutter.)
Will M. Farr <farr@mit.edu>**20070823130442] 
[Fixed bug where tags were being constructed in increasing order, but heap property expected decreasing tags.
Will M. Farr <farr@mit.edu>**20070823220816] 
[Added gradient, jacobian to deriv-lang.ss.
Will M. Farr <farr@mit.edu>**20070904214029] 
[Added scribble documentation.
Will M. Farr <farr@mit.edu>**20070904214109] 
[Extra doc for jacobian.
Will M. Farr <farr@mit.edu>**20070904221242] 
[Better documentation for gradient and jacobian.
Will M. Farr <farr@mit.edu>**20070904221816]