Reviewed and edited the text for reply to JE

I made a few corrections and modifications to the text. Just moved some
stuff around, nothing too big.

The larger changes were:
1. Adding a few sentences and links to the Github repo and saying that
the synthetics are there.
2. Replacing the links to the notebooks that said "here" with something
like "provided in the IPython notebook some_test_bla.ipynb".
The .ipynb_checkpoints don't need to be on git

These dirs are created by IPython for restoring closed files. They don't
need to be commited to version control.
Reformatted the sphere-cube comparison notebook

Separated text from headers so that not all text is bold face. Inserted
anomaly figures, added a note about where these notebooks come from and
that they run Fatiando. I'll include this note on all other notebooks
from now on.
add the pdf files with the authors response to JE
Merge pull request #8 from birocoles/review-leo

Review the author responses to JE