FindCython: allow the user to specify dependencies
Add csympy.pxd as the dependency to csympy_wrapper
Use Teuchos::RCP in the wrappers
Implement Integer
Deallocate the objects

This resets the RCP instance to null, which causes the underlying object's
reference count to be decreased, possibly deallocating it.

Without this patch, the RCP gets deallocated when it runs out of scope, which
sometimes happens late or never (in the Cython generated code, the RCP sits
inside a struct). This patch sets it to null, so we deallocate the C++ object
when the Python object gets deallocated, which is the right time to do it.
Add initial implementation of Basic.__add__()

So far we only return the string representation of the result.
Add a test for x+y
Return Python object from Basic.__add__()
Raise an exception when we cannot convert a class
Implement Basic.__mul__
Add more tests
Implement the == operation
Implement the != operation
Better syntax
Implement sympify() and use it in __mul__
Better handling of __mul__
Enable a test
Test for types in __mul__
Add tests for sympify()
Create SympifyError exception and test it