final clean up of python package tutorial

Overall: this is FANTASTIC. I tried to do a very thorough sweep through, read all files, check all links, etc. Here are the final crumbs:

[ ] minor: README.md does not conform to its own described format 😄
[x] somewhere (near the beginning) say something about "Use Python 3.5+ unless you have a very compelling reason to use Python 2.7. Because Python 2.7 support for some of the critical tools we rely on (e.g. Pandas, Numpy) is being phased out, the lab can no longer officially support any Python 2.7 tools or setups." The preferred approach is to make sure your package is compatible with Python 3.5+ (i.e. 3.5 and any stable releases subsequent to 3.5).
[x] README has minor typos (e.g. under LICENSE: MIT License; Under Tutorials: Then, in terminal...; )
[x] modify CONTRIBUTING.md to be for a generic lab package rather than hypertools
[x] is sphinx needed in requirements.txt? maybe that should be a developer option? it looks like it's part of docs/doc_requirements also. what about requiring numpy and adding an "add_array" function?
[x] add some text to examples/README.txt
[x] in docs/conf.py it looks like the file is for hypertools-- remove reference to hypertools (replace with name of example package) and update other parts of the file accordingly
[x] is the index.rst file right? looks like it might be for a different project?
[x] in docs/README.md, instructions for installing the requirements should say "Inside CDL-tutorials/packages/sample_package/docs run pip install -r doc_requirements.txt" (reference doc_requirements instead of requirements)
[x] in setup.py, we had discussed some of modifying the requirements definitions inside setup.py to allow for different optional install options (e.g. dev, doc, etc.). may want to add something here for that...e.g. perhaps referencing the doc/doc_requirements.txt file? First link under description for setup.py in README.md doesn't work (needs to be updated?). Same with requirements.txt.
[x] add instructions for adding a "build passing" or "build failing" badge (i.e. TravisCI status badge) to readme (under Tests?)
[x] .travis.yml -- can remove Python 2.7; Also, under TravisCI instead of "python 2 and 3" I think we should say "Python 3.5+"
[x] Under Releases, what's the "(2.0.0 at the time of writing this)" part refer to? Remove?
[x] Final "Fin" --> italicize?

Fin

ContextLab / CDL-tutorials

final clean up of python package tutorial #29