Introduce default assignment simplifications

There are many simplifications in pystencils that are usually not applied. They can be applied now by using a simple argument in the configuration.

Fixes #39 (closed)

pystencils_tests/test_astnodes.py

@@ -84,14 +84,18 @@ def test_loop_over_coordinate():
 
 @pytest.mark.parametrize('default_assignment_simplifications', [False, True])
 def test_sympy_assignment(default_assignment_simplifications):
-    import logging
-    logging.basicConfig(level=logging.DEBUG)
+    from pystencils.simp.simplifications import apply_sympy_optimisations
+
     assignment = SympyAssignment(dst[0, 0](0), sp.log(x + 3) / sp.log(2) + sp.log(x ** 2 + 1))
 
     config = ps.CreateKernelConfig(default_assignment_simplifications=default_assignment_simplifications)
     ast = ps.create_kernel([assignment], config=config)
     code = ps.get_code_str(ast)
 
+    if default_assignment_simplifications:
+        assignments = apply_sympy_optimisations([assignment])
+        print(assignments)
+        
     if default_assignment_simplifications:
         assert 'log1p' in code
         # constant term is directly evaluated