Add remark/, sdcv.remark, sdcv utility wrapper.

zsh/remark_syntax/(README.md)
	-Add a directory for regex-highlighting rule files for the
	`remark` utility, with an explanatory `README.md`.

zshrc, zsh/remark_syntax/sdcv.remark
	-Add `remark` highlighting for the `sdcv` utility, and implement
	a wrapper function `def()` to simplify its usage.