Bounds2 should be used instead of the duck-typed coords

[jonathanolson]

Multiple places have code like:

var coords = {};
coords.leftX = ...
coords.topY = ...
coords.rightX = ...
coords.bottomY = ...

I'd recommend instead using Bounds2, which is made for that purpose:

var bounds = new Bounds2( leftX, topY, rightX, bottomY );

which can then be accessed with:

bounds.left
bounds.right
bounds.top
bounds.bottom

For code review #29

[AshrafSharf]

The object literal is used because the Bounds2 doesn't have a setter for left or right so it forces us to create a new Bounds2 instance every time (for 1000s of particles) which degrades performance due to GC. However I have renamed "leftX" to "left". and made changes to top,right and bottom along the same lines which is consistent with the naming convention adopted by other scenery classes.
@jonathanolson Let me know if it is fine

[jonathanolson]

'left' and 'right' are aliases for 'minX' and 'maxX', would things be cleaner with using setMinX() and setMaxX()?

[AshrafSharf]

Replaced duckType object properties with Bounds2 instance for Texture and Vertext coordinates.
used the approach suggested in the previous comment(setMinX)

[jbphet]

This appears to have been fully addressed, closing.