Allow --template to take a URL argument.

MANUAL.txt

@@ -645,10 +645,10 @@ General writer options
     output.  For `native` output, this option causes metadata to
     be included; otherwise, metadata is suppressed.
 
-`--template=`*FILE*
+`--template=`*FILE*|*URL*
 
-:   Use *FILE* as a custom template for the generated document. Implies
-    `--standalone`. See [Templates], below, for a description
+:   Use the specified file as a custom template for the generated document.
+    Implies `--standalone`. See [Templates], below, for a description
     of template syntax. If no extension is specified, an extension
     corresponding to the writer will be added, so that `--template=special`
     looks for `special.html` for HTML output.  If the template is not

src/Text/Pandoc/App.hs

@@ -381,7 +381,7 @@ convertWithOpts opts = do
                                      "" -> tp <.> format
                                      _  -> tp
                       Just . UTF8.toString <$>
-                            (readFileStrict tp' `catchError`
+                            ((fst <$> fetchItem tp') `catchError`
                              (\e ->
                                  case e of
                                       PandocIOError _ e' |