#68 CARRY4 internal connectivity request

[Neil Steiner]

Request to add CARRY4 internal connectivity to the architecture database or associated structure. The motivation is for calculating accurate timing paths that pass through carry elements.

Dependencies:
CO3/COUT: S3, CO2, DI3
O3: S3, CO2
CO2: S2, CO1, DI2
O2: S2, CO1
CO1: S1, CO0, DI1
O1: S1, CO0
CO0: S0, X, DI0
O0: S0, X
X: CIN or AX or constant (1 or 0)