IBCM number fix

Pursuant to #21, fix the bit numbering in IBCM slides and book chapter to match the usual convention: the high-order bits have higher numbers, that is, we go 15 downto 0 rather than 0 up to 15 (or 1 up to 15).

(Held from fix during IBCM material as a fix for F2014; merged to final-exam-time repo state.)