Display with self

[tailhook]

Builds upon #6, and probably fixes syntax

[colin-kiegel]

Looks good to me - You could change the README example, too. I suggest:

diff --git a/README.rst b/README.rst
index 34e0665..ee6a83c 100644
--- a/README.rst
+++ b/README.rst
@@ -32,7 +32,7 @@ Here is the comprehensive example:
             }
             IoAt(place: &'static str, err: io::Error) {
                 cause(err)
-                display("Error at {}: {}", place, err)
+                display(self_) -> ("{} {}: {}", self_.description(), place, err)
                 description("io error at")
                 from(s: String) -> ("some string",
                                     io::Error::new(io::ErrorKind::Other, s))

[colin-kiegel]

PS: Thx. :-)

[colin-kiegel]

I think the branch display_fn could be deleted on github