add De Bruijn patterns

adds command "D[go]" to generate cyclical patterns of length provided in next arg, or to find offset in the pattern of a number. Works for both big and little endian hosts with big or little endian guests.

closes #900 
What about using "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" instead?