Misc updates

A bunch of miscellaneous updates:

- Finish the getting-started document so that it contains some useful pointers at least. It's still not great, but it's at least something.
- Refresh the scipy/numpy building instruction pages from the wiki.
- Remove outdated pieces of text at various points.
- Move all pages having to do with Scipy/Numpy the libraries under `scipylib/`.
- Add links to `scikits.appspot.com` and PyPI to "topical software".

With these changes, I don't see anything that's significantly better in the scipy.org wiki. I think swapping the front page to this one could be possible.