Make a reproject tutorial

[cdeil]

@astrofrog – How about a tutorial IPython notebook on reproject to make it easier for people to find it and try it out?

I could take the main examples from http://reproject.readthedocs.org/en/latest/ and do this today.
Keep it short and link to the reproject, wcsaxes and healpix docs at the end.

[kelle]

This would be great but it would be better if it include some lower level content as well. We need a basic WCS tutorial. Could you include this as well: #10 ?