With the {F...} syntax, render non-images as links

Summary:
We render a huge picture of a PDF for PDFs right now, etc. This is hella dumb.

Also allow users to force this rendering style, and change the link name.

Test Plan: Uploaded image and non-image files, used layout=link and name=....

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T1040

Differential Revision: https://secure.phabricator.com/D2006

src/docs/userguide/remarkup.diviner

@@ -296,10 +296,13 @@ You can set file display options like this:
 
 Valid options are:
 
-  - **layout** left (default), center, right, inline
+  - **layout** left (default), center, right, inline, link (render a link
+    instead of a thumbnail for images)
   - **float** If layout is set to left or right, the image will be floated so
     text wraps around it.
   - **size** thumb (default), full
+  - **name** with `layout=link` or for non-images, use this name for the link
+    text
 
 = Embedding Media =