[fpp-to-xml] Escape special characters in XML attributes

[bocchino]

XML attributes may not include the character <. We should replace it with <. Several other characters are also not allowed in attributes. They are listed below.

[timcanham]

Additional comment: While the XML autocoders are still in the mix, all the disallowed XML tokens should be replaced in the format specifiers.

They include: >,<, &, ",'

[bocchino]

Good to know! Do you know what the replacements are? Currently we are replacing < as < and " as ".

[bocchino]

It looks like there may be an answer here: https://stackoverflow.com/questions/5709232/how-do-i-include-etc-in-xml-attribute-values.

[timcanham]

That's the set!