Fix in the docs of gridder.interp_at

The docstring was saying that it returns 3 arrays when in 
fact it returns only one (the interpolated).
Removing logger from cookbook
Fixed 'print' on cookbook
Merge pull request #71 from hbueno/logger

Removing logger from cookbook
Cleaned Makefile

Removed unused targets, old comments, PHONY declarations
Removed the neprism module

This was a test module using numexpr to forward model prisms in gravmag.
Didn't give adequate speedups and wasn't worth adding as a dependency.
Missing needed phony tags in Makefile

The test target needed to be PHONY because of the test dir.
Add Cython .c files and break build in 2 parts

Separate the generation of .c files by Cython and building the C
extensions. setup.py now takes a --cython argument that triggers Cython
conversion. If not set, will just build the given .c files.

To avoid problems with readthedocs, modules try to import the Cython
mods and upon failure substitute functions with a mock that raises an
exception.

Docs of gravmag.prism is now mostly in the module docstring because all
functions are in the Cython module. Can still get the docstrings of the
functions but not in the built docs.

TODO: Need to include the .c files in Manifest
Include .c files in MANIFEST

Needed so that the Cython generated .c files are included in source
distributions.
Merge branch 'master' into cython
Removed unused pylintrc file
Removed old unsupported harvest script
Merge branch 'master' into cython
Build before testing in Makefile

Added build as a dependency for test
Removed cython and mayavi install in Travis

They were unused. Also moved some things around in the commands.
Sphinx build had to be before install in Travis

Because the build fails with the compiled binaries.
Travis badge now points to master branch

To avoid showing a lot of build failures from incomplete branches.
Set the virtualenv flag for Travis again

This time I added comments so that I don't forget why it was there.
Added links to pull requests in changelog

Filled in missing entries and linked the entries to the corresponding
PRs that implemented them. Also put links to the ones that the team made
for the first time.
Merge pull request #75 from leouieda/cython

Include Cython generated .c files in the repo