re-enable PyMethodDef declarations of Python methods in cdef classes as we cannot currently generate CyFunctions for cpdef methods

enables line tracing etc.

directly call into CPython's Unicode writers to format float/int values, rather than going all the way through PyObject_Format() and its method lookups

fix docs example: getArea instead of undefined getLength

Replace "int(val) == 0" by "not val" for gdb.Value instances