Implements transliteration without using the PECL extensions.
Transliterations are done character-by-character, by looking up non-US-ASCII characters in a transliteration database.
The database comes from two types of files, both of which are searched for in the PhpTransliteration::$dataDirectory directory. First, language-specific overrides are searched (see PhpTransliteration::readLanguageOverrides()). If there is no language-specific override for a character, the generic transliteration char