I18n Support and some interface improvments

fix: https://github.com/henrique2010/precise_distance_of_time_in_words/issues/2

Also this contains a fix to make sure that the time distence is always
positive and make the second parameter optional, so you can call it like
precise_distance_of_time_in_words(12) # => "12 Seconds"

If you call it with objects that response to_time this method is beeing
used.
adding some specs and update gemspec
Merge pull request #4 from toxix/i18n-support

I18n Support and some interface improvments