ForceChangeRate calculation operators

[Chippychap]

Many units have additional calculation operators which do not require you to work with unitless values.
However, there are no additional operators for the ForceChangeRate unit.

I propose adding the following operators:

public static Force operator *(Duration left, ForceChangeRate right); //Duration.extra.cs
public static Force operator *(ForceChangeRate left, Duration right); //ForceChangeRate.extra.cs
public static Duration operator /(Force left, ForceChangeRate right); //Force.extra.cs

[angularsen]

@Chippychap Sounds good to me, would you be willing to attempt a PR? I'm happy to assist.

[Chippychap]

I am certainly willing to do this. Will look into it this weekend.

[angularsen]

Great!