docs: Break up 'Basic Resources' XML section
docs: Break up 'Basic Resources' XML section

We had a bit too many elements crammed in there. Separate it into different
headings:

- CPU Allocation (<vcpus>)
- CPU Tuning (<cputune>)
- Memory allocation (<memory> and <currentMemory>)
- Memory backing (<memoryBacking>)
- Memory tuning (<memtune>)
- Numa tuning (<numatune>)
- Block I/O tuning (<blkiotune>)

taget/libvirt,olafhering/libvirt,leilihh/libvirt,datto/libvirt,trainstack/libvirt,zhlcindy/libvirt-1.1.4-maintain,shugaoye/libvirt,jeckersb/libvirt,shugaoye/libvirt,novel/fbsd-libvirt,VenkatDatta/libvirt,zhlcindy/libvirt-1.1.4-maintain,leilihh/libvirt,emaste/libvirt,agx/libvirt,andreabolognani/libvirt,agx/libvirt,leilihh/libvirt,elmarco/libvirt,emaste/libvirt,rmarwaha/libvirt1,novel/fbsd-libvirt,andreabolognani/libvirt,foomango/libvirt,dumbbell/libvirt,foomango/libvirt,soulxu/libvirt-xuhj,agx/libvirt,eskultety/libvirt,usc-isi/libvirt,trainstack/libvirt,novel/fbsd-libvirt,iam-TJ/libvirt,shugaoye/libvirt,wiedi/libvirt,shugaoye/libvirt,dumbbell/libvirt,wiedi/libvirt,cbosdo/libvirt,wiedi/libvirt,soulxu/libvirt-xuhj,VenkatDatta/libvirt,dumbbell/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,warewolf/libvirt,jfehlig/libvirt,trainstack/libvirt,foomango/libvirt,eskultety/libvirt,novel/fbsd-libvirt,danwent/libvirt-ovs,zippy2/libvirt,bjzhang/libvirt,wiedi/libvirt,jardasgit/libvirt,jeckersb/libvirt,libvirt/libvirt,jardasgit/libvirt,libvirt/libvirt,datto/libvirt,leilihh/libvirt,emaste/libvirt,usc-isi/libvirt,iam-TJ/libvirt,wiedi/libvirt,rmarwaha/libvirt,libvirt/libvirt,fabianfreyer/libvirt,emaste/libvirt,cbosdo/libvirt,warewolf/libvirt,eskultety/libvirt,trainstack/libvirt,elmarco/libvirt,nertpinx/libvirt,usc-isi/libvirt,kantai/libvirt-vfork,nertpinx/libvirt,rmarwaha/libvirt,dumbbell/libvirt,zippy2/libvirt,cbosdo/libvirt,bjzhang/libvirt,warewolf/libvirt,jardasgit/libvirt,rmarwaha/libvirt,datto/libvirt,siboulet/libvirt-openvz,rlaager/libvirt,emaste/libvirt,jardasgit/libvirt,zippy2/libvirt,soulxu/libvirt-xuhj,zhlcindy/libvirt-1.1.4-maintain,bjzhang/libvirt,elmarco/libvirt,siboulet/libvirt-openvz,rmarwaha/libvirt,leilihh/libvirt,iam-TJ/libvirt,crobinso/libvirt,jeckersb/libvirt,trainstack/libvirt,kantai/libvirt-vfork,iam-TJ/libvirt,cbosdo/libvirt,foomango/libvirt,jeckersb/libvirt,datto/libvirt,zippy2/libvirt,taget/libvirt,siboulet/libvirt-openvz,rlaager/libvirt,jardasgit/libvirt,crobinso/libvirt,kantai/libvirt-vfork,andreabolognani/libvirt,zhlcindy/libvirt-1.1.4-maintain,danwent/libvirt-ovs,fabianfreyer/libvirt,dumbbell/libvirt,crobinso/libvirt,taget/libvirt,rmarwaha/libvirt1,trainstack/libvirt,novel/fbsd-libvirt,rmarwaha/libvirt,nertpinx/libvirt,taget/libvirt,nertpinx/libvirt,siboulet/libvirt-openvz,rlaager/libvirt,emaste/libvirt,novel/fbsd-libvirt,foomango/libvirt,agx/libvirt,libvirt/libvirt,shugaoye/libvirt,rlaager/libvirt,jeckersb/libvirt,novel/fbsd-libvirt,datto/libvirt,iam-TJ/libvirt,crobinso/libvirt,olafhering/libvirt,warewolf/libvirt,cbosdo/libvirt,rmarwaha/libvirt1,wiedi/libvirt,warewolf/libvirt,kantai/libvirt-vfork,wiedi/libvirt,olafhering/libvirt,olafhering/libvirt,warewolf/libvirt,jfehlig/libvirt,elmarco/libvirt,eskultety/libvirt,agx/libvirt,nertpinx/libvirt,rmarwaha/libvirt,danwent/libvirt-ovs,rmarwaha/libvirt1,iam-TJ/libvirt,bjzhang/libvirt,rmarwaha/libvirt1,danwent/libvirt-ovs,kantai/libvirt-vfork,emaste/libvirt,soulxu/libvirt-xuhj,iam-TJ/libvirt,eskultety/libvirt,VenkatDatta/libvirt,jeckersb/libvirt,siboulet/libvirt-openvz,elmarco/libvirt,fabianfreyer/libvirt,novel/fbsd-libvirt,novel/fbsd-libvirt,trainstack/libvirt,VenkatDatta/libvirt,rlaager/libvirt,jfehlig/libvirt,jeckersb/libvirt,andreabolognani/libvirt,dumbbell/libvirt,leilihh/libvirt,andreabolognani/libvirt,usc-isi/libvirt,VenkatDatta/libvirt,rmarwaha/libvirt1,danwent/libvirt-ovs,soulxu/libvirt-xuhj,taget/libvirt,bjzhang/libvirt,jfehlig/libvirt,warewolf/libvirt,zhlcindy/libvirt-1.1.4-maintain,usc-isi/libvirt