function releaseArray(array) {
  Physics.util.clearArray( array );
  if (arrayPool.length < maxPoolSize) {
    arrayPool.push(array);
  }
}
Physics.util.filter( collection, fn( value, index, collection ) ) -> Array
- collection (Array): Collection of values to test
- fn (Function): The test function
- value (Mixed): The value to test
- index (Number): The index of value in collection
- collection (Array): The input collection

Test an array of values against a test function
and return another array of values for which
the test function returns true.