Fix makefile to build cargoized examples

[farcaller]

Makefile is currently broken from #318 and will not build examples as expected. The whole its existence is slightly questionable now, as it's basically pre and post-processing around cargo. Maybe we need to make a simple wrapper around cargo anyway (sounds like a reasonable option given how cargo isn't that much cross-build friendly)?

[mcoffin]

I agree, especially since a lot of that processing is platform-specific. Personally, however, I find the listing files incredible for debugging, so I would want a version kept around anyways.

The other thing it does is hide our slightly-not-idiomatic "feature" usage in cargo. I think it would be worth making an RFC for refactoring how we go about separating out all the various platforms and stuff (which really should be done alongside a better, more well-thought-out implementation of #286). It might even be prudent to actually set a time and get together at some point on IRC and talk though it. I've banged my head at coming up with a completely-idiomatic adaptable solution and it's actually a relatively hard problem to solve while still adhering to the 0-overhead philosophies of Rust.

Sorry I've been scarce lately too, though I'm actually working on some zinc stuff right now with adapting the ioreg crate to be useful in fpga environments as well as on bare metal. Might even warrant ioreg becoming it's own "project" down the road.

[farcaller]

docs updated to use proper cargo commands in #351