Remove trailing whitespace
Allow more flexible translations for “empty” values

The “empty” value actually means any value, ie. any hour, any minute,
any month or any day of week, day of month, etc. Translations of “any”
for each of these types differ in many languages.

By specifying a language translation for `empty_day_of_month`, one can
now customize these translations. If no custom per-type translation is
available, the default one for `empty` will be used.
Update the minified version of the script
Merge pull request #9 from mitio/more-flexible-translations

More flexible translations for "empty" values
Extract translations into separate files

This way if an application does not need a particular translation, the
file can just be omitted and the overall file size will be reduced.

Adding new translations becomes easier this way, too.

Many modern web frameworks support asset file bundling (concatenation
and minification) and multiple files should not be an issue.
Fix an accidental typo causing a syntax error
Set the default language to English
Remove trailing whitespace
Log an error and return if translations are missing