Various fixes and changes as suggested from the comments on proposal.
* The function to create the KML code now uses the SimpleXML class.
* Function to create KML code is now in the magic __toString() method under the XML_KML_Create
* Removed the save() method
* Implemented constructers and destructers
* Implemented one-class-per-file rule adding Main.php KML/Place.php and KML/Style.php
* Changed class name KML to XML_KML_Create
* Changed class name KMLPlace to XML_KML_Place
* Changed class name KMLStyle to XML_KML_Style
* Implemented set*() methods on XML_KML_Style and XML_KML_Place that validate input
* Code now adheres to PHPCodeSniffer standards