Remove asm/ folder

- Until it's needed again
- Removed all asm/* files from index
- Keep the asm folder with .keep file
- Add asm folder to .gitignore
Extract error handling from wp_tegen to wp_error

Add wp_error module:
- Move all error/exception-based code from wp_tegen to wp_error
- Update wp_tegen to include wp_error
- Rename wp_error typedefs and structs for consistency
- Reorder parameters of wp_error_notify for consistency

wp_graphics:
- Minor correction to #endif comment in header