Better gps API
Added 'A1. Blink an LED' notebook and presentation
Fixed url for pullup resistor diagram
Added custom.css stylesheet for presentation
Futher API improvements

* ewb.gps() returns a gps object
* ewb.radio(freq) returns a radio object
Added setup.py and module cleanup
Merge branch 'setup' into notebooks
merge fix
Merge remote-tracking branch 'ewb/notebooks' into notebooks
Mention setup.py in README.md
Started Worksheet notebook & changes to slides
WIP on revision of notebooks