Canvas Context Documentation

I had forgotten what each field of $canvasContext was supposed to be. That's what documentation is supposed to be for.

Now there's documentation.

Signed-off-by: Seth Battis <SethBattis@stmarksschool.org>
User Sync

Users are now syncing (use your profile URL -- http://<canvas instance url>/about/<user id>), resolving [this issue](https://github.com/smtech/canvas/issues/16). I'm still not syncing my own calendar until the [RegEx filter](https://github.com/smtech/canvas/issues/20) is built...

However, groups are broken (probably "still" rather than a new development). [Some sort of permissions error.](https://github.com/smtech/canvas/issues/22) Not. A. High. Priority. (For now.)

Signed-off-by: Seth Battis <SethBattis@stmarksschool.org>