Added time shift parameter

[MisterProper9000]

I ran into a problem that the library doesn't have the ability to start the transition from the values of object's properties that were on the transition at the moment t, which can be difficult to calculate, especially if the transition rule is complex (for example, outInBounce).

In my case, it was needed to initialize the scales of objects that approach the player from the horizon and grow up nonlinearly and which have to be between the player and the horizon when scene appears.

So I added a time shift parameter to all transitions (except dissolve) which defines initial value of object's property when the transition starts.

A short explanation of how time shift parameter behaves and interacts with the delay parameter in transition with duration T:

• if time shift > 0 then transition begins with the value of the object's properties that would have been reached by the object by time equals time shift with an unmodified transition and lasts for T - time shift ms.
• if both are defined and both > 0 then one calculation of object's properties is performed, then it waits for delay ms, and then transition continues for T - time shift ms.
• if time shift < 0 then trasition behaves as if delay is defined and equals |time shift|.
• if both are defined and delay > 0 and time shift < 0 then transition waits for delay + |time shift| ms and then starts from the initial values of object's property and lasts for T ms.

These code changes will not affect any existing projects.

[CLAassistant]

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