'gpio' smoke test

Verifies that the library physically work. It requires the user to connect two GPIO pins together and provide their pin number at the command line.

Example output running on a Raspberry Pi:

$ gpio-test 12 6
Using drivers:
  - bcm283x
  - rpi
  - sysfs-gpio
  - sysfs-spi
  - sysfs-i2c
Using pins and their current state:
- GPIO12: In/High
- GPIO6: In/High

Testing GPIO6 -> GPIO12
  Testing base functionality
    GPIO12.In(Float)
    GPIO6.Out(Low)
    -> GPIO12: In/Low
    -> GPIO6: Out/Low
    GPIO6.Out(High)
    -> GPIO12: In/High
    -> GPIO6: Out/High
  Testing edges
    GPIO12.Edges()
    GPIO6.Out(Low)
    Low <- GPIO12
    GPIO6.Out(High)
    High <- GPIO12
    GPIO6.Out(Low)
    Low <- GPIO12
    GPIO12.DisableEdges()
  Testing pull resistor
    GPIO6.In(Down)
    -> GPIO12: In/Low
    -> GPIO6: In/Low
    GPIO6.In(Up)
    -> GPIO12: In/High
    -> GPIO6: In/High
Testing GPIO12 -> GPIO6
  Testing base functionality
    GPIO6.In(Float)
    GPIO12.Out(Low)
    -> GPIO6: In/Low
    -> GPIO12: Out/Low
    GPIO12.Out(High)
    -> GPIO6: In/High
    -> GPIO12: Out/High
  Testing edges
    GPIO6.Edges()
    GPIO12.Out(Low)
    Low <- GPIO6
    GPIO12.Out(High)
    High <- GPIO6
    GPIO12.Out(Low)
    Low <- GPIO6
    GPIO6.DisableEdges()
  Testing pull resistor
    GPIO12.In(Down)
    -> GPIO6: In/Low
    -> GPIO12: In/Low
    GPIO12.In(Up)
    -> GPIO6: In/High
    -> GPIO12: In/High