(#23) add a new option "--continue"

When specifying "--continue" Grunt will keep running tasks even
if one fails (similar to "--force") but will exit with an error
code if any of the tasks failed.
(#23) changelog
Merge branch 'feature-0.5.x/23-add-continue-option' into release-0.5.x

* feature-0.5.x/23-add-continue-option:
  (#23) changelog
  (#23) add a new option "--continue"

Conflicts:
	CHANGELOG.md