Add handling for the newer FGDC ISO Metadata standards

[JeffJacobson]

The code currently only has special handiling for CSDGM metadata XML. Newer standards have since been adopted by the FGDC since CSDGM was created. While basic HTML formatting should still work, the element names in headings will not be replaced with their long name equivalents.

[JeffJacobson]

I think ISO-19139 is what ArcGIS supports.