Modify DoxygenUtility plugin layout; add README.md

Add:
	vim/scripts/DoxygenUtility/README.md
		-Add a documentation README to the plugin root.

	vim/scripts/DoxygenUtility/ftplugin/c.vim
		-Move `syntax` and `highlight` commands from
		`plugin/DoxygenUtility.vim`'s `s:ConfigurePlugin()` to a `c`
		ftplugin file.

Rem:
	vim/scripts/DoxygenUtility/plugin/DoxygenUtility.vim
		-`s:ConfigurePlugin()` was disassembled and moved to
		`ftplugin/c.vim`, so the file was left empty of code.