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
Added code minus tests
Added basic vector tests
Merge branch 'master' of https://github.com/sympy/sympy into basicvector
Added Del operator tests
Merge branch 'master' of https://github.com/sympy/sympy into basicvector
Rectified bugs, made improvements in __new__ code
to update
Merge branch 'master' of https://github.com/sympy/sympy into basicvector
Added doctests
Merge branch 'master' of https://github.com/sympy/sympy into basicvector
Rectified doctests
Rectified bugs for simplify and trigsimp