DPSF Particle Vertex Interface

In order for the particles to be drawn the properties required to visualize the particles must be copied to a vertex buffer.  A Particle Vertex struct must be defined that can hold the particle properties required to draw the particles.  The vertex buffer will then be defined as an array of these Particle Vertex structs.  All Particle Vertex structs must implement the IDPSFParticleVertex interface, which requires that VertexElements and SizeInBytes properties must be defined.