Uses 'build' option if no option is passed to '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, `build` 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. Check `output` panel to see the result.
4. If the build was sucessful, just click in any file with `run_*` preffix in `/scripts` folder and voilá!
```

In addition to we have simplified instructions, we get rid of a limited number of IDEs supported by CMake with focus only on C++ whereas in reality Nupic is a python project with a few c++ extensions.


I'm confused because the title of this PR is to use the `build` option by default, not `develop`. :confused: