Update setup.py

Now `setup.py` checks if no option was passed, i.e. if `setup.py` is the only option. If it's the case, `develop` is passed by default. This is very useful when a developer wish build the project directly from an IDE.

This should work well both with IDE and shell interface. After merged we can replace the current CMake instructions (https://github.com/numenta/nupic/wiki/Development-Tips) to these simplified ones.

```
These following instructions will work in the most Python IDEs:
1. Open your IDE.
2. Open a project specifing the $NUPIC repository folder as location. 
3. Click with mouse right button on `setup.py` file listed on project files and select `Run` command on popup menu. This will call the build process.
4. After build process done, just click in any file with `run_*` preffix in `/scripts` folder and voilá!
```