Fix all the stuff you broke last night...

In particular the `pi_revision` thing in PiGPIOPin, all the stuff @lurch
picked up in `pins/data.py` (thank goodness *someone's* watching!), and
make all those links pointing to "Notes" point somewhere useful like
"Pin Numbering"...

docs/examples/robot_keyboard_2.py

@@ -12,9 +12,9 @@ devices = [InputDevice(device) for device in list_devices()]
 must_have = {i for i in range(1, 32)}
 must_not_have = {0}
 devices = [
-    device
-    for device in devices
-    for keys in (set(device.capabilities().get(ecodes.EV_KEY, [])),)
+    dev
+    for dev in devices
+    for keys in (set(dev.capabilities().get(ecodes.EV_KEY, [])),)
     if must_have.issubset(keys)
     and must_not_have.isdisjoint(keys)
 ]

docs/recipes.rst

@@ -9,6 +9,8 @@ library. Please note that all recipes are written assuming Python 3. Recipes
 *may* work under Python 2, but no guarantees!
 
 
+.. _pin_numbering:
+
 Pin Numbering
 =============
 
@@ -18,8 +20,9 @@ configurable.
 
 .. _RPi.GPIO: https://pypi.python.org/pypi/RPi.GPIO
 
-Any pin marked ``GPIO`` in the diagram below can be used for generic
-components:
+Any pin marked "GPIO" in the diagram below can be used as a pin number.  For
+example, if an LED was attached to "GPIO17" you would specify the pin number as
+17 rather than 11:
 
 .. image:: images/pin_layout.*