Adds I2C implementation and basic accelerometer crate.

[tcr]

This commits the I2C interface and an accelerometer crate that can read acceleration values.

Note that API design questions should be surfaced on #29. Our goal is to get our interfaces working and tested asap, but design the ergonomics more carefully before 1.0.

[johnnyman727]

[Dr-Emann]

Rc<Mutex<T>> is probably not what you want. Rc is not shareable across threads. If you want to lock the port to a single thread, you can use Rc<RefCell<T>> (RefCell is basically a mutex for a single thread). If you want it to be shareable across threads, you want Arc<Mutex<T>> instead.

[tcr]

@Dr-Emann Agreed; I'll swap that for this release.

[johnnyman727]

Did you add this just for clarity? I don't think I needed this but maybe my setup was just different.

[tcr]

Yeah, mine required it. Guess it doesn't hurt to be specific when cross-compiling.

[johnnyman727]

I'm not experienced enough to comment on that API design as-is but I'm curious about why the accel-mma84 driver is living within the tessel-rust repo. Shouldn't that be an addition to its own repo?

[tcr]

@johnnyman727 I think we did something like this when we started with T1; basically we had all the code in one repo to help evolve the API all at once, and broke out the modules once the API settled down. I expect that to happen here.

Also, whoops, did not notice the Rust version of the MMA84 code. Probably past the point of using it now though :(