Add recursive solver for Vigenere
Add factory for A-Z alphabet
Rename Alphabet#sanitize
Add alphabet spec
Update yaml examples for specs

We have to differentiate between examples that
are meant to preserve characters in cleartext that
are not present in the alphabet (e.g. punctuation)
from those that are meant to discard it. This commit
provides some naming conventions and a small
testing infrastructure for that purpose.
Re-run all specs when a yaml file changes
Add specs for preserving non-alphabetic characters
Add README
Clean up vigenere