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 
that works too. I just used that charset to compare against a known good implementation. Will switch to the [A-Za-z0-9] set when I move it into the "wo" command tonight.