Allow defining time based on point paths and speeds

For example, AV2's remote boomerang or mist movement. The latter is exit movement, which is currently supported only for straight lines. The former involves the player staying in position (or falling) while the boomerang moves from point to point. An ideal way to represent a curving path and a return would be to detail the points and speeds between them, e.g.

    path: [Spot, [A, B], Other Spot, [C, D], Spot]
    speeds: [mist2, mist2, mist2, ret]

which is to say, "path" can include either raw coordinates or in-area spot names, and speeds is all the names of the movements we'd use to calculate time.

For movements, this would be similar to #187 except for speeds replacing movement to allow for (or require) defining all of them.