Rustdoc should include default methods in trait implementation documentation

[sfackler]

For example, there's no mention of insert in the TreeMap documentation since it's a default method on MutableMap: http://static.rust-lang.org/doc/master/extra/treemap/struct.TreeMap.html

[thestinger]

cc @alexcrichton, @cmr

[sfackler]

Javadoc just has a list of "Methods inherited from foo" (e.g. http://docs.oracle.com/javase/7/docs/api/java/util/TreeMap.html) which seems fine.

[alexcrichton]

I agree!