Default value of pull in Pin constructor is None

Hardware-API.md

@@ -127,7 +127,7 @@ def pin_handler(pin):
 
 Creates and initilizes a pin.
 
-`pin = Pin(id, mode, pull=Pin.PULL_NONE, *, value, drive, slew, alt, ...)`
+`pin = Pin(id, mode, pull=None, *, value, drive, slew, alt, ...)`
 - `id`: mandatory and positional. `id` can be an arbitrary object (among possible value types are: int (an internal Pin ID), str (a Pin name), tuple (pair of [port, pin]))
 - `mode`: is mandatory and positional (can be kw). Specifies pin mode:
   - `Pin.IN` - Pin configured for input; there's additional requirement that, if viewed as output, pin was in high-impedance state. This requirement is almost universally satisfied by any MCU.