Verifier.php code partially documented
Small correction on README.md
Document rules methods
Verifier.php code fully documented
Merge branch 'dev'
Release v0.5.1

- Verifier.php code fully documented
- Verifier constructor now support a optional parameter to configure init value for $test variable
- New built-in validators: isEmpty(), isNotEmpty()
- New rule: containAny()
- Small code optimizations