Add input/power-switching lib functions, add Wii-U tablet interface…

+ The Wii-U interface (optimized for the Wii-U tablet NetFront-based browser) must be run off a web server offering PHP support (if you have a Mac from the past few years your OS almost certainly offers a capable built-in Apache, and if you're a Linux nut, you know what to do -- Windows users, suggest you "run for the hills," to the tune of getting a copy of XAMPP -- search for XAMPP on Google and good luck!)
+ This commit adds the pvRebel_setPower and pvRebel_setSource functions to the lib, to (respectively) allow you to set receiver's power on (true as 2nd arg) and off (false as 2nd arg), and to allow you to set receiver's current input source (see the pvRebel_getSource lib function for now for a list of input numbers and use the two numeric bytes as a string as the second argument to indicate the input you want to switch to).