Add a new URI parsing library to QEMU. The code has been borrowed from
libxml2 and libvirt.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>