[miclqdco] Letters to keep far apart

Take the N most common words and identify words that differ by only one letter.  Enumerate the letter pairs which should be kept far apart on a keyboard layout.

Inspired by problems with (if of) (this thus) (*es *ed) on QWERTY soft keyboards.

Alternatively, given a keyboard layout, score it against the top N most common words.  First, enumerate the adjacent letters in the layout, then count the number of pairs of words that differ by only one adjacent pair, then two adjacent pairs to break ties, etc.