Add new type HoverResult to contain the results of hovering

This makes testing hovers easier as well as allows us to do more things with the
results if needed.

crates/ra_lsp_server/src/main_loop/handlers.rs

@@ -441,7 +441,7 @@ pub fn handle_hover(
     let res = Hover {
         contents: HoverContents::Markup(MarkupContent {
             kind: MarkupKind::Markdown,
-            value: info.info,
+            value: info.info.to_markup(),
         }),
         range: Some(range),
     };