changed raise_exception to reject, changed unit tests, models, messages
updated docs for changie raise_exception to reject
Merge branch 'develop' into feature/issue-458-reject-stmt
updating test
Merge branch 'develop' into feature/issue-458-reject-stmt
updating tests
Merge pull request #1003 from stan-dev/feature/issue-458-reject-stmt

Feature/issue 458 reject stmt