Escape URLs in literals in reference manual

This prevents the URLs from being rendered as clickable links in the
generated HTML.

Author: sbrannen

src/docs/asciidoc/core/core-resources.adoc

@@ -404,11 +404,11 @@ objects:
 | Loaded from the classpath.
 
 | file:
-| `file:///data/config.xml`
+| `\file:///data/config.xml`
 | Loaded as a `URL` from the filesystem. See also <<resources-filesystemresource-caveats>>.
 
 | https:
-| `https://myserver/logo.png`
+| `\https://myserver/logo.png`
 | Loaded as a `URL`.
 
 | (none)