Use wheels on travis

Care is taken to use a numpy wheel whose version matches the scipy/astropy wheels.

This is an alternative to https://github.com/astropy/package-template/pull/37 that also addresses #24 and hopefully addresses the issue that @cdeil had with https://github.com/astropy/package-template/pull/37.

An example of the builds it produces on travis is at https://travis-ci.org/astropy/ccdproc/builds/21107695

There are at least few things that should be done before this is merged, if this seems like the way to go:

- [x] Move the wheels on my server to either of the astropy wheelhouses (I'm willing to host, but adding a third place to look doesn't seem helpful).
- [x] Address omission of ``-w`` in sphinx build
- ~~[ ] Confirm what the minimum coverage expectations are for affiliated packages.~~

The script that produced these wheels on an Ubuntu VM isn't included in this PR, though I'm happy to share it.

EDIT may 7 2014: cross off coverage expectations for packages