Please update documentation for setting properties that are functions.

Column settings that take functions as values need to be better documented.
For example for compareFunction there is no indications for what the input will be nor what the output should be. (if anyone is wondering here is the default compare :
`protected static COMPARE = (direction: any, a: any, b: any) => {
if (a < b) {
return -1 * direction;
}
if (a > b) {
return direction;
}
return 0;
}
`)

This is also the case for the property filterFunction.