implemented more array arithmetic operators
added sum and prod arithemetic functions
Merge branch 'master' of https://github.com/pele-python/pele into array_operators
added overall operators tests
Merge branch 'master' of https://github.com/pele-python/pele into array_operators
remove a very old playground directory
remove the obsolete directory
Merge branch 'master' of github.com:pele-python/pele
fixes
Fixed confusing error message and lowered Cython requirement.
Merge pull request #31 from olenz/master

Fixed confusing error message and lowered Cython requirement.
removed binary operators and renamed tests
Merge branch 'master' of https://github.com/pele-python/pele into array_operators
Merge pull request #29 from smcantab/array_operators

Array arithmetic operators and other arithmetic functions
update c++ example potential

There were several changes made to the c++ backed that were not
reflected in the example
add a test for LJCutAtomList

this tests the AtomListPotential, which is an alternate to
SimplePairwisePotential
add test for BLJ

this also tests CombinedPotential
add analytical hessian to CombinedPotential and AtomListPotential
rename tests to comply with nosetests

nosetest tests discovery won't recognize tests in files named
_test_object.py

also, nosetests with run a test twice if it imported somewhere else,
e.g. if it was imported in __init__.py.
Merge pull request #33 from js850/fix_nosetests

fix a few bugs with nosetests