Allow the creation of remote pins easily with PiGPIOPin. Also changes DefaultPin to a pin_factory callable which accepts the input pin number.
Warnings about non-physical pins, and period specification for sin/cosine waves in tools
Related to @lurch's comments on #148, this PR contains a database of pins for each Pi revision, along with various other bits of miscellany (I might've gotten a bit carried away here...). Any corrections/extensions welcome!