add kind system and kind-checking pass to rustc

[graydon]

rustc has no kind system, now kind-checking pass. add one.

[graydon]

Initial cuts landed in commit 63f74f3, a11bb40, 3e63fdc, etc. Still wip.

[pcwalton]

Going to mark this as no longer a 0.1 blocker now that we have the basics in. Please feel free to re-mark if necessary.

[marijnh]

Moving this over to #1177.