Added weakkeydict
WeakRef dictionary by itself is essentially the same as no cache. Added
a fixed length deque to keep track of some keys
most of the key,value pairs we want to cache are not weak-referenceable,
get around this limitation by using both weakkey and weakvalue dicts
fixed typo in return statement
Implemented Python 3 functools.lru_cache as a class decorator compatible
with py2 and 3
Removed locks and some if statements to improve performance
add variable size to lru_cache through environment variable SYMPY_CACHE_SIZE
cache_debug now appropriately handles SYMPY_CACHE_SIZE
Various items listed as autoclass which should be autofunction
The latest version of livereload does not use the -b option
Move the printing part of the tutorial after the gotchas and basic operations

Pretty printing is not used in the tutorial until after these sections, and
they are more important than printing.
Include simplification
Don't use bullets for the "whet your appetite" section

It just looks bad.
Wording
Note that the printing options are in the settings (which are hidden by default)
Some wording on the "Why SymPy?" section
Spell functions as function() in the printing tutorial
Don't use `` in section titles in the simplification part of the tutorial
Write functions as function() in the simplification section of the tutorial

I have used the convention that Python functions are written as function(),
but SymPy objects (like sin) are not.
Grammar