Restore the SIV and CMAC modes, export also the cbcMac

This provides a conditionally (and by default used) stripped down version of CPoly which results again in reasonable compile times (smaller than 1 second in my system). This can be disabled by using the flag ALL_CPOLYS. The elected block lengths for CPoly cover most of the known block ciphers.

It also restores the SIV and CMAC modes of operation and reexports the cbcMac one. This is largely an undo of the commit 500aa7f41a3f605fac9f8125561e8bd93c2f3714 so you may want to move some of the stuff to the Classes instead.