HTML entities method is not multibyte safe

Problem/Motivation

The method obfuscateEmail() of class ObfuscateMailHtmlEntity iterates over the value's bytes, not its charaters.
While this might not be an issue with email addresses (since they are plain ASCII in most cases), it can be a problem when an additional link label is passed to getObfuscatedLink(). If this string contains characters that are encoded with more than one byte (e.g., German umlauts), those characters will be broken.

Proposed resolution

Use a different method for iterating over the string, e.g. as proposed here.
Use mb_ord() instead of ord() for encoding characters.