fixed typo in SumoCollisionDetect example comment (thanks davidskeck via GitHub)
Pushbutton lib: fix to work properly with multiple instances
Pushbutton lib: improved debouncing logic and reduced width of PrevTimeMillis vars. I'm hesitant to make them 1 byte because that means the functions would wrongly think 15 ms hasn't elapsed yet if the function is called after e.g. 266 ms.
Merge pull request #1 from pololu/master

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