[Feature Request] Markdown Preview

[M00NJ]

Since Cosmic Edit can open and edit .md files, a preview mode would be a useful feature, especially when working with big markdown tables. Currently I use Apostrophe for this, but having it covered by the default Text Editor would expand it's use case and eliminate the need for a second app. This could be made accessible over the view menu in the header bar, or a separate toggle that appears when editing .md files.