Expose a public API
Allow :format option lookup via I18n or DATE_FORMATS hashes

First attempts to find the passed in :format option in:
- I18n time.formats.{format}
- I18n date.formats.{format}
- Time::DATE_FORMATS
- Date::DATE_FORMATS
Else, returns the passed in :format option straight up or, if blank, uses the
default format: '%B %e, %Y %l:%M%P'.
Disallow Proc return values from DATE_FORMATS hashes

Also, turn untranslatable Procs into strings that pass through unchanged,
as before.
Rewrite of time_format method for clarity

Tidy up white space
Add details of new format options to README
Optimize format lookup: Symbol -> I18n/DateFormat; String -> strftime
Tidy up README. Make i18n localization file path explicit.
Use a constant for the default strftime format
Condense format as symbol docs
Test public API. h/t @mikestone
Document API
Merge branch 'global'
local_time 0.3.0