Update Guardfile

Watch for changes in .yml files
Move days and months definition into the YAML file

Values are kept under keys:
+ :'date.standalone_abbr_day_names'
+ :'date.common_abbr_day_names'
+ :'date.standalone_day_names'
+ :'date.common_day_names'
+ :'date.standalone_abbr_month_names'
+ :'date.common_abbr_month_names'
+ :'date.standalone_month_names'
+ :'date.common_month_names'
Small code cleanup
Update .gitignore
Remove obsolete TODO (as there's no failing tests)

Remove calls to I18n#reload! as Polish#init_i18n does it already
Bump version