fix grunt task
Update readme
Update changelog and package files
chore(async): Improve loading configuration, assert and ensure invalid ones.

- If the loader is not valid, it should not be used.
- If `invokeLoading` will be invoked, it is possible that no async loader is available (empty array).
- Assert the loader builder function returns a valid function.
feat(translateProvider): missingTranslationHandler

- Support for custom handling of missing translations via
  $translateProvider.missingTranslationHandler(handlerFn)
Add missing var statement
Merge pull request #25 from knalli/improve-loader

chore(async): Improve loading configuration, assert and ensure invalids
Merge branch 'canary' of github.com:PascalPrecht/ng-translate into canary
Merge pull request #27 from jamesandres/missing-translate-handler

feat(translateProvider): missingTranslationHandler