accept 'y', 'yes', and 't' for true, and 'f', 'no', and 'n' for false.
Merge pull request #490 from craigcalef/master

accept 'y', 'yes', and 't' for true, and 'f', 'no', and 'n' for false.
Fixes #491, this moves to the unified str_to_bool and extends it with extra boolish strings