Add ability to suggest corrections to mispellings

[lannonbr]

Related to rooseveltframework/roosevelt#955, it would be useful to have functionality to suggest existing config options if you misspell something. To do this I think you'd just need to take the misspelled word, all of the available config options at that layer in the config, and then run something to calculate the Levenshtein distance and output a better error with close words.