Add :at_least_one_present_validator message to en.yml (was hard-coded in
at_least_one_present_validator.rb).

Fix the call to to_sentence: It only had last_word_connector but also needs two_words_connector in
case there are only two items in the array.

Add tests for AtLeastOnePresentValidator.
Add :must_have_at_least_10_digits message to en.yml.
Add missing :year_invalid and :date_invalid messages to en.yml.
Namespace the YearValidator to be like all the other validators.
Allow min and max to be passed as options to YearValidator
Add missing tests for YearValidator
Add activemodel and sqlite3 as development dependencies since some tests require actual ActiveRecord
models.
Add missing tests for DateValidator.
Fix the date format given in the date_invalid message. It claimed that mm/dd/yyyy was the expected
format, but ActiveRecord actually interprets dates in the dd/mm/yyyy format instead (without some
effort/monkey patching to change that default).
Change the default expected_format to 'yyyy-mm-dd'. Add an :expected_format option in case you want
to override that.