docs/library/pyb.Pin: Fix out-of-context paragraphs, and AF_PP typo.

Remove out of context callback paragraph, it was part of the wipy docs.
And move the paragraph about PULL_UP/PULL_DOWN resistor values to within
the init() method docs.  Also fix pull-pull -> push-pull.

Signed-off-by: Chris Mason <c.mason@inchipdesign.com.au>

docs/library/pyb.Pin.rst

@@ -58,16 +58,6 @@ an ordinal pin number:
 You can set ``pyb.Pin.debug(True)`` to get some debug information about
 how a particular object gets mapped to a pin.
 
-When a pin has the ``Pin.PULL_UP`` or ``Pin.PULL_DOWN`` pull-mode enabled,
-that pin has an effective 40k Ohm resistor pulling it to 3V3 or GND
-respectively (except pin Y5 which has 11k Ohm resistors).
-
-Now every time a falling edge is seen on the gpio pin, the callback will be
-executed. Caution: mechanical push buttons have "bounce" and pushing or
-releasing a switch will often generate multiple edges.
-See: http://www.eng.utah.edu/~cs5780/debouncing.pdf for a detailed
-explanation, along with various techniques for debouncing.
-
 All pin objects go through the pin mapper to come up with one of the
 gpio pins.
 
@@ -107,7 +97,7 @@ Methods
         - ``Pin.IN`` - configure the pin for input;
         - ``Pin.OUT_PP`` - configure the pin for output, with push-pull control;
         - ``Pin.OUT_OD`` - configure the pin for output, with open-drain control;
-        - ``Pin.AF_PP`` - configure the pin for alternate function, pull-pull;
+        - ``Pin.AF_PP`` - configure the pin for alternate function, push-pull;
         - ``Pin.AF_OD`` - configure the pin for alternate function, open-drain;
         - ``Pin.ANALOG`` - configure the pin for analog.
 
@@ -117,6 +107,10 @@ Methods
         - ``Pin.PULL_UP`` - enable the pull-up resistor;
         - ``Pin.PULL_DOWN`` - enable the pull-down resistor.
 
+       When a pin has the ``Pin.PULL_UP`` or ``Pin.PULL_DOWN`` pull-mode enabled,
+       that pin has an effective 40k Ohm resistor pulling it to 3V3 or GND
+       respectively (except pin Y5 which has 11k Ohm resistors).
+
      - *value* if not None will set the port output value before enabling the pin.
 
      - *alt* can be used when mode is ``Pin.AF_PP`` or ``Pin.AF_OD`` to set the