x-samp extensions

SAMP uses the idea of extensible vocabularies, in which items are labelled with a key string. Keys in the namespace samp (i.e. ones which start samp.) are reserved as well-known and defined in standard itself. Developers are free to define keys in other namespaces as they wish. Keys in the special x-samp namespace are used for those keys that are proposed for possible introduction into the standard in the future. Developers are encouraged to list such keys here, with an explanation of their purpose.