Consider adding string transformations

[ohader]

see https://github.com/tgalopin/html-sanitizer/blob/master/src/Sanitizer/StringSanitizerTrait.php#L19-L37

• probably integrate as well (source uses MIT license)
• see Integrate ideas from OWASP in terms of validation and security tgalopin/html-sanitizer#6
• credit https://github.com/tgalopin