scholmd reader no longer treats "@done" at the end of line as citations

this syntax is often used to mark a task item as done, made popular with Taskpaper
scholmd: allow displayMath labels on new line to be in braces
resolve ambiguity between link refs and citations

now scans link references for possible citations first (possibly bad style?)
scholmd: x-refs only parse if reference exists

this change also allows the use of plain x-refs without the brackets pairs [].

closes #3 for now