Suggestion: use single cross-OS list of disallowed filename characters

[dge8]

The current list of disallowed filename characters is OS-dependent. However a common situation nowadays is sharing a folder of Markdown notes between multiple OSes using a cloud storage provider. Some CSPs handle disallowed file characters better than others.

Suggestion: use a single list of disallowed filename characters that meets the requirements of all common OSes (Mac, Linux, Windows), or provide a command-line option for this (e.g. --filenamecompat [auto|win|unix|all]).