Engine 5.15 released

Engine5.15

NEED TO ADD CALL BACKS TO VIEWER SUBS (NULLED FOR NOW)

Bugs fixed in this release
==========================
Re-wrote some parts of AudioManager to attempt to fix some inconsistences

an experimental "fix" added to limit box bouncing when gravity active - which curbs the over application of velocity on the bounce

changes in this release
=======================

AudioManager - added some callbacks for effects ending
KeyboardBuffer - new class to buffer input from XNA keyboard to allow typing (which was very difficult to do before I added this)
EngineManger - added some functionality

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AudioManager
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PlayEffect, PlayManagedEffect - all version can now specify a callback subroutine executed when the sound effect is stopped. This can allow you to use the ending of a sound effect to start a game mode. For these callbacks to execute safely they should run code using engineM.StateChange = subName so it is executed after all pending updates.

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KeyboardBuffer
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Active - when true keyboard buffer is active, default is false (no keyboard buffer)

GetBuffer - retrieves the current contents of the keyboard buffer

GetBufferAndFlush - retrieves the current contents of the keyboard buffer and then clears it

Flush() - clears the current contents of the buffer

RemoveLast() - removes the last character entered into the buffer, use this with your own checks for backspace key

SpecifyKeyMatchingPairs() - allows you to create your own set of valid keys and their display characters

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EngineManager
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StateChange - added, allows you to specify a subroutine to run at the end of current update. This is to be used when you need to change mode during event handlers and sprite handlers, so you don't get weird conflicts, which you mostly get away with but not always.