Add Suretax.configuration#mode and #production.
Default Suretax::Api::Request#data_year and #data_month based on configuration.production?
Refactor Concerns::Validatable to make use of the various Suretax constants.

Version bump.
Merge pull request #37 from bqsoft/WAVE-752_add_mode_to_configuration

Add Suretax.configuration#mode and #production.