Returns the version of the asset postprocessor.

When the script is recompiled, if a version change is detected, the assets associated with this asset postprocessor will be reimported.

	class TexturePostProcessor : AssetPostprocessor
	{
		// Bump this number to make textures reimport after modifying the post processor below.
		private uint m_Version = 0;
		public override uint GetVersion() {return m_Version;}
		public void OnPostprocessTexture(Texture2D tex)
		{
			Color[] pix = tex.GetPixels();
			for (int i = 0; i < pix.Length; i++)
			{
				pix[i] = pix[i] * 0.5f;
			}
			tex.SetPixels(pix);
			tex.Apply(true, true);
		}
	}