reify
__repr__ for unify.core classes
rewrites first commit
add test for strategy
top_down parametrizes children and op
tree traversal functions for unify/core
add logpy test
computations first commit
add edges
add CompositeComputation and unique function
inputs/outputs are attributes, not functions
actual tests. composite in_out solution
add reverse dict and toposort functions

Conflicts:

	sympy/utilities/iterables.py
	sympy/utilities/tests/test_iterables.py
add dag and toposort methods
add more complex test
add variables property
docstrings
__add__ and CompositeComputations can initialize
add str methods
remove composite testing class