Add wait functions to PID class

[ssejrog]

Is your feature request related to a problem? Please describe.

The PID class was forgotten about and should be unforgotten.

Describe the solution you'd like

Add a wait, wait_until, and is_at_position(?) functions. These functions should be used in chassis.wait() and chassis.wait_until().

Additional context

Having the wait functions in the Drive class is bad. They should be in the PID class, and the necessary modifications should be made in the chassis.wait() and chassis.wait_until() functions. For example, when the left side is within small_thresh for the required amount of time, the code shouldn't exit until the right side has also completed this.

interfered (#16) should be moved to these new functions. chassis.interfered should be set when the left and right have interfered.

by defaulting the exit condition constants to 0 except for small_exit, only the small exit should run. when the other values are set to numbers that aren't 0, they should be introduced.

chassis exit conditions need to stay backwards compatible

[ssejrog]

Still needs to be incorporated to the drive, comments, and a wiki page.