Update to libWiringPi 2.15

ADD: Constants:
- SOFT_PWM_OUTPUT
- SOFT_TONE_OUTPUT
- PI_MODEL_A
- PI_MODEL_B
- PI_MODEL_NAMES (array)
- PI_REVISION_NAMES (array)
- PI_COMPUTE_REVISION_NAMES (array)

ADD: piBoardId function
ADD: softPwmStop function
ADD: softToneStop function