Refactored formatter class #2359 which works with or without intl extension. Use PHP format patterns alsow with intl. Class is compatible with previous version.
Namespace corrected #2359
Typo in function call #2359
remove comment lines in asRelativeTime
#2359 testcases adapted and compatibility to old tests improved
#2359 one test failed in Travis because standard medium date format is different in Travis then on my locale PC.
#2359 Bugfix in normalizeDatetimeValue after regression test
Merge branch '2359-formatter-refactored' of https://github.com/Erik-r/yii2-1 into Erik-r-2359-formatter-refactored

* '2359-formatter-refactored' of https://github.com/Erik-r/yii2-1:
  #2359 Bugfix in normalizeDatetimeValue after regression test
  #2359 one test failed in Travis because standard medium date format is different in Travis then on my locale PC.
  #2359 testcases adapted and compatibility to old tests improved
  remove comment lines in asRelativeTime
  Typo in function call #2359
  Namespace corrected #2359
  Refactored formatter class #2359 which works with or without intl extension. Use PHP format patterns alsow with intl. Class is compatible with previous version.
refactored date formatting functions

- removed unformat methods, they do not belong here
- removed db format, which is also not purpose of this class
- refactored the whole set of methods to be simpler and better
  maintainable

More unit tests needed.
remove FormatDefs file

we do not want our own i18n database.
When this kind of data is needed intl extension is a requirement.
update
guide-zh-CN/rest-quick-start.md translated.
guide-zh-CN/rest-routing.md translated.
guide-zh-CN/rest-rate-limiting.md translated.
guide-zh-CN/rest-error-handling.md translated.
line breaking fixed.
symbol modified.
guide-zh-CN/rest-response-formatting.md translated.
guide-zh-CN/rest-versioning.md translated.
Fix typos and semantic errors in Serbian translation