Update to python3 and add pipenv

Pipfile

@@ -0,0 +1,14 @@
+[[source]]
+url = "https://pypi.python.org/simple"
+verify_ssl = true
+name = "pypi"
+
+[packages]
+markdown-include = "==0.5.1"
+mkdocs = "==0.15.3"
+pymdown-extensions = "==1.1"
+
+[dev-packages]
+
+[requires]
+python_version = "3.6"

README.md

@@ -21,42 +21,13 @@ Once a PR is merged into master, the latest version will automatically be deploy
 ## Installation of [mkdocs](http://www.mkdocs.org/)
 
 ```sh
-brew install python # if you don't have pip already
-[sudo] pip install -r requirements.txt
+brew install python3 # if you don't have pip already
+brew install pipenv
+pipenv --three
+pipenv shell
+pipenv install
 ```
 
-_Note: If you use `sudo` to run `pip`, you might need to use the `-H` flag of `sudo`._
-
-### Troubleshooting
-
-Due to a bug in `pip` trying to uninstall El Capitan's version of `six` (protected by SIP) when needing a new one, you may encounter the following error during `pip install -r requirements.txt`:
-
-```sh
-OSError: [Errno 1] Operation not permitted: '/tmp/pip-[…]-uninstall/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/six-1.4.1-py2.7.egg-info'
-```
-
-In this case, just [install `six` using the `--ignore-installed` flag first before retrying](https://github.com/pypa/pip/issues/3165#issuecomment-146666737):
-
-```sh
-[sudo] pip install --ignore-installed six
-[sudo] pip install -r requirements.txt
-```
-
-
 ## Adding a Python dependency
 
-Likely, to add a [Markdown extension](https://pythonhosted.org/Markdown/extensions/).
-
-1. Install with `pip install <some extension>`
-2. Add <some extension> to [requirements-to-freeze.txt](requirements-to-freeze.txt).
-3. Run `pip freeze > requirements.txt` to update the exact requirements.
-
-### Why requirements-to-freeze.txt?
-
-Based on [A Better Pip Workflow](http://www.kennethreitz.org/essays/a-better-pip-workflow),
-`requirements-to-freeze.txt` and `requirements.txt` provide a similar experience
-to Gemfile and Gemfile.lock, respectively.
-
-`requirements-to-freeze.txt` lets you pick out the top level packages the
-project depends on, while `requirements.txt` exactly specifies all of the
-dependencies and subdependencies for repeatable builds.
+Likely, to add a [Markdown extension](https://pythonhosted.org/Markdown/extensions/), install it with `pipenv install <some extension>` after making sure the virtualenv is loaded (`pipenv shell`).

circle.yml

@@ -1,11 +1,12 @@
 machine:
   python:
-    version: 2.7.11
+    version: 3.6.0
   ruby:
     version: 2.3.0
 dependencies:
   pre:
-    - pip install -r requirements.txt
+    - pip install pipenv
+    - pipenv install
 test:
   override:
     - bundle update