[Libvir] request for libvirt documentation improvement

The documentation of libvirt doesn't indicate which functions are for Xen or QEMU or both. The only way to know that, is by searching in libvirt sources. It would be interesting for libvirt users to add in the documentation, for each function, a mention such as "QEMU only", "Xen(TM) only", "QEMU and Xen(TM)", etc.. Regards. Libvirt 0.2.3 functions dedicated to QEMU only: virConnectListDefinedNetworks virConnectListNetworks virConnectNumOfDefinedNetworks virConnectNumOfNetworks virDomainGetAutostart virDomainSetAutostart virNetworkCreate virNetworkCreateXML virNetworkDefineXML virNetworkDestroy virNetworkFree virNetworkGetAutostart virNetworkGetBridgeName virNetworkGetName virNetworkGetUUID virNetworkGetUUIDString virNetworkGetXMLDesc virNetworkLookupByName virNetworkLookupByUUID virNetworkLookupByUUIDString virNetworkSetAutostart virNetworkUndefine Libvirt 0.2.3 functions dedicated to Xen(TM) only: virConnectGetMaxVcpus virConnectGetType virDomainAttachDevice virDomainCoreDump virDomainDetachDevice virDomainGetMaxMemory virDomainGetSchedulerParameters virDomainGetSchedulerType virDomainPinVcpu virDomainReboot virDomainSetMaxMemory virDomainSetMemory virDomainSetSchedulerParameters virDomainSetVcpus