First cleanup and documentation pass on read_parallel
First cleanup and documentation pass on read_parallel

To explain my thought process on adding PIN_COUNT:
1. Magic numbers are bad, so having "7" as our loop condition is not
very readable.
2. If someone ever changes the pin array(s) without changing PIN_COUNT,
the compiler SHOULD warn them, preventing silent failure in the form of
not reading pins past the 8th array element.

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