Use newlayerinfo() to allocate and initialize a layer_info structure and
associated sub-structures.

    struct Layer_Info *NewLayerInfo( void );

You must call this function before attempting to use any of the other
layers functions described below.  When you have finished with a
layer_info structure, use disposelayerinfo() to deallocate it.

    void DisposeLayerInfo( struct Layer_Info *li );

This function deallocates a layer_info and associated structures
previously allocated with newlayerinfo().