[mdufxexb] 8 button keyboard

Inspired for a touchscreen keyboard for a wide tablet.

4 buttons on each side (8 total), labeled 0 through 7, to be operated by thumbs.  Letters and other actions are button sequences, for example 8^3=512.  Octal input of a Unicode value also possible as a last resort.

Middle area contains an undo-last-button-press button (not a backspace button, because this one allows backspacing a partial button sequence), redo last action (simulating repeatedly pressing a button on a full keyboard), echo of the partial button sequence so far.  Undo-last across a full-character boundary only works if the program receiving keystrokes understands backspace, and there were no intervening cursor repositioning (perhaps by touching a point on the screen).  Similarly, navigation actions, etc.  Things can get hairy for control actions: you probably need application support for, say, undoing a cut action.

And a help button, possibly voice help.