quick2wire.gpio Pin classes now follow same API conventions as those in the mcp23x17 module.
GPIO pins now have open() and close() methods and act as their own context managers. They export
the pin to userspace on open() and reset the pin state and unexport it on close().

THIS IS A BREAKING API CHANGE
Removing imports and calls to exported() which are no longer necessary.
Updated getting-started doc to reflect new API
Renamed _IOPin to Pin. Pass function to __init__ that maps index to SoC pin number.
This is fist step to introducing pin banks for on-board GPIO
PinBank abstraction for on-board GPIO.

Different pin-banks are exported from the quick2wire.gpio module:

  gpio        - GPIO pins numbered 0..8
  pi_header_1 - the pins on the Pi's header 1, except power and
                those labeled do-not-use, numbered 1..26
  pi_broadcom_soc - pins identified by Broadcom SoC pin number
updating the getting started with GPIO doc
renamed quick2wire.gpio.gpio to gpio_breakout
updating getting started doc to reflect new name for gpio_breakout
Renamed gpio_breakout -> pins
updated docs to match rename
Merge pull request #22 from npryce/gpio-improvements

quick2wire.gpio Pin classes now follow same API conventions as those in ...