make OStream's inputs type-specific

e.g. unsigned long long instead of uint64_t
buttons manage toggling

SW will send packets listing whether buttons have been toggled. Upon
receiving an ACK for a button, it will mark the button as not-toggled,
and broadcasting so.

also modified SW buttons TX frame signature.
fix post-compilation/symbol loading of optimized build

Apparently, you need to end all streams to nu::OStream with an nu::end,
or else MPLAB throws a "Symbol loading error."