Move src/* to hwloc/ to prepare for netloc addition

Also move tests/* to tests/hwloc/

Utils were already in specific directories.
Add netloc

Library source files go under netloc/* on the side of hwloc/
Headers, tests, utils are added near hwloc ones.

doc/main.doxy is added, which includes the former hwloc.doxy and the new netloc.doxy
Will be better inntegrated in next commit so that we don't touch hwloc too much here.

Netloc is enabled by default when supported (basically everywhere except
on Windows and Solaris), can be disabled with --disable-netloc.
It builds a separate libnetloc shared library (so that we can stabilize the
netloc ABI without breaking the hwloc ABI, at least for now).
If you disable netloc or do not include/link with netloc, you get a "normal" hwloc.

netloc test files are not included because some of them are big.
They may go to a separate repository (we may want to do that for
hwloc's tests/linux/ at some point if 1.7MB is considered too much).

hwloc/master is now branch v2.0
doxy: integrate hwloc.doxy and netloc.doxy through a main.doxy

Add a global introduction, and the common install instructions
and strip things from hwloc and netloc sections.
Add references in all directions to ease things.

One thing that remains to be updated/merged is the bug report section,
we'll fix this later once the actual merge is done and once we know
where netloc bug reports should be sent.