Rewrite validators using schemas
Move definition test to validators tests
Fix all tests
Remove redundant lower()

Thanks @Natim @tarekziade for reviewing !

::notes::

    I  didn't find the regex version more readable :

    strip_perm = re.sub(r'^[\-\+](.+)$', r'\1', value).lower()
Remove dead code introduced in 3c7432b078f (fixes #236)
Merge pull request #237 from spiral-project/236_fix_duplicated_errors

Prevent duplicate errors in response (fixes #236)