Add basic support for cython extension types

Signed-off-by: Michael Buesch <m@bues.ch>
insns: Add cimport

Signed-off-by: Michael Buesch <m@bues.ch>
insns: Declare status-word variable

Signed-off-by: Michael Buesch <m@bues.ch>
Convert instruction classes to Cython extension types

Signed-off-by: Michael Buesch <m@bues.ch>