Allow empty lines in lint doc examples

This makes sure that empty lines in lint examples are preserved.

It also fixes the documentation for the invalid_ref lint, which was not
shown because of an extra newline before the lint declaration.

clippy_lints/src/attrs.rs

@@ -97,12 +97,11 @@ declare_lint! {
 /// // Good (as inner attribute)
 /// #![inline(always)]
 ///
-/// fn this_is_fine_too(..) { ... }
+/// fn this_is_fine(..) { ... }
 ///
 /// // Good (as outer attribute)
 /// #[inline(always)]
-/// fn this_is_fine(..) { ... }
-///
+/// fn this_is_fine_too(..) { ... }
 /// ```
 declare_lint! {
     pub EMPTY_LINE_AFTER_OUTER_ATTR,

clippy_lints/src/invalid_ref.rs

@@ -13,7 +13,6 @@ use utils::{match_def_path, opt_def_id, paths, span_help_and_lint};
 /// ```rust
 /// let bad_ref: &usize = std::mem::zeroed();
 /// ```
-
 declare_lint! {
     pub INVALID_REF,
     Warn,