escapeStringXml vs escapeStringXML

[andythehood]

The PR [fix661] that added support for the escapeStringXml() function named it with XML in uppercase, i.e. escapeStringXML().

According to the Stdlib reference, it should be the former.

I don't know which one is correct (I assume the former for consistency with the other escapeString* functions), but the documentation and the implementation need to be consistent.

Or overload them so both forms work.