Add pelican-based webpage

[bgrant]

Add a pelican-based website for DistArray. It will allow us to easily add content in the future. To see the generated website, see http://docs.enthought.com/distarray.

Requires the python package pelican. Pelican lets us add content as restructuredText, Markdown, or AsciiDoc. I also use the pelican theme pelican-bootstrap3.

I've split up and re-used .rst files from the docs as much as possible for the webpage. I've integrated @kwmsmith's overview.rst document from a branch of his.

As part of this PR, I add a www directory to docs and rearrange the docs directory a bit. I put all of the sphinx documentation into a sphinx subdirectory of docs, and I add another subdirectory for talks.

If you have pelican installed, you should be able to go to the docs/www directory, type

make html
make serve

And go to localhost:8000 to see the website locally. make github will build and push the website to our gh-pages branch (requires ghp-import). See the README document in docs/www for more.

Some content highlights

1. Erick's DistArray logo
2. features.ipynb added as one of our pages (updated and improved in another PR)
3. Five DistArray talks added to the Talks page
4. Release notes added as a page

[kwmsmith]

@bgrant this is awesome -- thank you for putting this together, and for adding some polish.

Looks like Travis is breaking from the known issue with the update to NumPy 1.9. Does not appear to affect this PR's content.