Merge pull request #1 from pbugnion/master

Changes leading up to v0.1 release.
DOC: Created requirements file for building docs.

Read the docs needs to be told that numpydoc is necessary.
BLD: Moved requirements file to root directory.

We actually need to build the whole package to get autodoc documentation
to work on read the docs. I've added dependencies necessary to construct
the package and moved the requiements file to the base directory.
DOC: Added image source files for tutorial to repo.
DOC: Updated links in tutorials.

The links for images were broken following the rename build -> img for
the directory holding images.