In this commit:
* Updated the DDA draft to version 0.4;
* Broke out the pointer accessor function into a version for real blocks and a version of complex blocks, mirroring the vsip_blockfind() and vsip_cblockfind() API;
* Added the layout as a parameter to the required_buffer_size function;
* Removed the separate layout type for complex types to be consistent with the VSIPL++ specification.