VCForPython27.msi fixed dataviz requirements installation issues on Win8.1

Using Windows 8.1, on "Step 0" of the "dataviz" tutorial, requirements installation line:

```
>pip install -r requirements
```

produced errors mentioning that a Visual C++ 9.0 compiler was needed. Reading further down:

```
>pip install numpy
```

produced nearly identical errors.

A search revealed a new-ish [C++ compiler for Python 2.7](http://www.microsoft.com/en-us/download/details.aspx?id=44266) released by Microsoft.

After running this installer, I deactivated the virtualenv and reactivated. Then, I ran `pip install numpy` successfully. matplotlib and geojson also worked.