bringing source up to date with latest HEAD
added 'exes' target to build just the rust programs
neaten up raw-blink to make use of write! macro a bit less awkward
remove parts-bin chapter for now -- error messages getting distracting
starting to sketch out 'rust whats the big idea' chapter
notes on relevant things I stumble upon
use native runtime types to implement gpio::Pin so I can get hold of the file descriptor, which is needed by epoll
Explain how user space GPIO works in Raspbian
Added a short chapter looking at the hello-world program.
naive button blink -- needs concurrency!