Implement Python module for wristband GPIO access

Does what it says on the tin. It will fix #31 (closed)

Documentation/pycardium/gpio.rst

+.. py:module:: gpio
+
+``gpio`` - GPIO Pins
+==========================
+The :py:mod:`gpio` module allows you to use card10's GPIO pins as input and
+output in your scripts.
+
+**Example**:
+
+.. code-block:: python
+
+   import gpio
+
+   gpio.set_mode(gpio.WRISTBAND_1, gpio.mode.OUTPUT)
+   gpio.write(gpio.WRISTBAND_1, True)
+   
+   gpio.set_mode(gpio.WRISTBAND_2, gpio.mode.INPUT | gpio.mode.PULL_UP)
+   state = gpio.read(gpio.WRISTBAND_2)
+   print("State of Wristband pin 2:", state)
+
+.. py:function:: gpio.set_mode(pin, mode)
+
+   Configure GPIO pin state.
+
+   :param int pin: ID of the pin to be configured.
+   :param int mode: An integer with the bits for the wanted mode set. Create your
+      integer by ORing :py:data:`gpio.mode.OUTPUT`, :py:data:`gpio.mode.INPUT`,
+      :py:data:`gpio.mode.PULL_UP`, :py:data:`gpio.mode.PULL_DOWN`.
+
+.. py:function:: gpio.get_mode(pin)
+
+   Get GPIO pin state.
+   
+   :param int pin: ID of the pin of to get the mode of.
+   :returns: An integer with the configure mode bits set.
+
+.. py:function:: gpio.write(pin, value)
+
+   Write a value to a GPIO pin.
+   
+   :param int pin: ID of the pin of to get the mode of.
+   :param bool value: New pin value.
+   
+.. py:function:: gpio.read(pin)
+
+   Read GPIO pin value.
+   
+   :param int pin: ID of the pin of to get the mode of.
+   :returns: Current value of the GPIO pin.
+
+.. py:data:: gpio.WRISTBAND_1
+
+   Pin ID for Wristband GPIO 1.
+
+.. py:data:: gpio.WRISTBAND_2
+
+   Pin ID for Wristband GPIO 2.
+
+.. py:data:: gpio.WRISTBAND_3
+
+   Pin ID for Wristband GPIO 3.
+
+.. py:data:: gpio.WRISTBAND_4
+
+   Pin ID for Wristband GPIO 4.
+   
+.. py:data:: gpio.mode.OUTPUT
+
+   Configures a pin as output.
+   
+.. py:data:: gpio.mode.INPUT
+
+   Configures a pin as input.
+   
+.. py:data:: gpio.mode:PULL_UP
+
+   Enables the internal pull-up resistor of a pin.
+   
+.. py:data:: gpio.mode:PULL_DOwn
+
+   Enables the internal pull-down resistor of a pin.