WIP: Allow changing key value separator beyond indentation

We have many ini-style configuration files which use : as key value
separator. We'd like to be able to manage them with ini_setting as well.
This here is a naïve first attempt in that direction.

Please note that despite the fact that this *should* match, it's failing
unit tests.. This is a work in progress.
Fix spec: predicates return booleans
Rebase/fix the flexible k/v separator.
Merge pull request #139 from mhaskel/flexible_key_val

Flexible key val