var_simplifier: removed a dependence on Meta by adding our own get_symbols() function.
Trimmed trailing whitespace
specializer: removed a dependency on Meta
utils: added get_fn_arg_id() to address the differences between function arguments representation in Py2 and Py3
optimizer: fixed a typo
optimizer: fixed the application of Name constructor
moved the base test case class to the tests folder
Eliminated dependency on meta

It is only required for tests now.
test_optimizer: added Py3 support to test_constant_propagation_fail()
test_specializer: added Py3 compatibility to exception handling
setup: added dependency on six
specializer: Py3 support for dict.iteritems
test_optimizer: added more accurate tests for division (with or without future.division)
optimizer: added Py3 support to builtins list
test_optimizer: added Py3 support to printing
optimizer: detecting enabled truediv
test_utils: added Py3 support (Py3 has additional arguments for some nodes)