Adding internal API reference links to the narrative docs

Sean Gillies

Hi all,

In the Rasterio quickstart guide I've added some links to API documentation. For example, see the "open()" link under the 2nd code block in I did this with the following ReST markup: :func:``. Sphinx has already indexed where is defined in the docs and completes the link. I hope you'll find this useful. Any such contributions that anybody would like to make would be gratefully received!

Note that the changes won't appear in the stable docs until we have another release.

Sean Gillies