Docs: Change all internal links to correct format

Resolves LP#1294347

I just deleted one link since I couldn't find any trace of where it was intended to go.

acquisitions/selection_lists_po.txt:
"or use the link:federated.txt[View/Place Orders] menu item in the catalog."

If anyone ever finds where that is supposed to go, let me know and I'll fix it.

Signed-off-by: Josh Stompro <github@stompro.org>
Signed-off-by: Remington Steed <rjs7@calvin.edu>