Allow silencing of non-string configuration warning #226

[owst]

This adds a new configuration entry, FIGARO_SILENCE_STRING_WARNINGS, which if set to true/'true' will silence warnings like WARNING: Use strings for Figaro configuration. 100 was converted to "100".

[hlascelles]

This change has been extracted and added (https://github.com/hlascelles/figjam/pull/8) to a fork and continuation of this repo, and a new gem called Figjam: https://github.com/hlascelles/figjam

Thank you @owst!