New function for converting MapX styles to SLD

A Styled Layer Descriptor (SLD) is an XML schema specified by the Open Geospatial Consortium(OGC) for describing the appearance of map layers. In particular, SLD files are used by GeoServer and QGIS.

A new function is now available in MapX, allowing to convert MapX styles to SLD files. This will make MapX even more compliant with international standards for geospatial information, and even more interoperable with other GIS software.