hwloc.h: trailing whitespaces
Add hwloc_get_numanode_obj_by_os_index()

And document that this function as well as hwloc_get_pu_obj_by_os_index()
are good at converting nodesets and cpusets into objects.
doc: move hwloc-hello.c to a new examples section
doc/examples: add an example of finding shared caches by looking at process binding
doc/examples: add an example of advanced memory binding and nodeset usage
doc/examples: add an example of cpubinding, bitmap API, cpusets
add some comments everywhere about doc/examples
README update