ikiwiki/ todo/ automatic use of syntax plugin on source code files

Wishlist: optionally use the syntax plugin automatically on source code files in the repository with recognized extensions or shebangs, and render them as though they consisted of an .mdwn page containing nothing but a single call to the syntax plugin with the file contents as the text argument and the recognized type as the type argument.

Together with the ability to have wiki-formatted comments, this would allow the use of ikiwiki for literate programming.