Address #1902: Converts example/flaskr to have a setup.py (#1945)

* Converts example/flaskr to have a setup.py

Makes the flaskr app easier to run, ex. workflow:
- pip install --editable .
- export FLASK_APP=flaskr.flaskr
- flask initdb
- flask run

Testing is also easier now:
- python setup.py test

* Fixed an import error in flaskr/tests

- the statement `import flaskr` caused errors in python3
- `from . import flaskr` fixes the issue in 2.7.11 and 3.5.1

* Better project structure and updates the docs

- Re-factors *flaskr*'s project structure a bit
- Updates docs to make sense with the new structure
  - Adds a new step about installing Flask apps with setuptools
  - Switches first-person style writing to second-person (reads better IMO)
  - Adds segments in *testing.rst* for running tests with setuptools

* Remove __init__.py from tests

- py.test recommends not using __init__.py

* Fix testing import errors

docs/tutorial/folders.rst

@@ -3,21 +3,25 @@
 Step 0: Creating The Folders
 ============================
 
-Before we get started, let's create the folders needed for this
+Before getting started, you will need to create the folders needed for this
 application::
 
     /flaskr
-        /static
-        /templates
+        /flaskr
+            /static
+            /templates
 
-The ``flaskr`` folder is not a Python package, but just something where we
-drop our files. Later on, we will put our database schema as well as main
-module into this folder. It is done in the following way. The files inside
-the :file:`static` folder are available to users of the application via HTTP.
-This is the place where CSS and Javascript files go.  Inside the
-:file:`templates` folder, Flask will look for `Jinja2`_ templates.  The
-templates you create later on in the tutorial will go in this directory.
+The application will be installed and run as Python package.  This is the
+recommended way to install and run Flask applications.  You will see exactly
+how to run ``flaskr`` later on in this tutorial.  For now go ahead and create
+the applications directory structure.  In the next few steps you will be
+creating the database schema as well as the main module.
 
-Continue with :ref:`tutorial-schema`.
+As a quick side note, the files inside of the :file:`static` folder are
+available to users of the application via HTTP.  This is the place where CSS and
+Javascript files go.  Inside the :file:`templates` folder, Flask will look for
+`Jinja2`_ templates.  You will see examples of this later on.
+
+For now you should continue with :ref:`tutorial-schema`.
 
 .. _Jinja2: http://jinja.pocoo.org/