small error code explanations improvements

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0033.md

@@ -24,4 +24,4 @@ dereferencing the pointer.
 You can read more about trait objects in the [Trait Objects] section of the
 Reference.
 
-[Trait Objects]: https://doc.rust-lang.org/reference/types.html#trait-objects
+[Trait Objects]: https://doc.rust-lang.org/reference/types.html#trait-objects

src/librustc_error_codes/error_codes/E0038.md

@@ -62,7 +62,7 @@ cause this problem.)
 In such a case, the compiler cannot predict the return type of `foo()` in a
 situation like the following:
 
-```compile_fail
+```compile_fail,E0038
 trait Trait {
     fn foo(&self) -> Self;
 }
@@ -183,7 +183,7 @@ fn call_foo(thing: Box<Trait>) {
 
 We don't just need to create a table of all implementations of all methods of
 `Trait`, we need to create such a table, for each different type fed to
-`foo()`. In this case this turns out to be (10 types implementing `Trait`)*(3
+`foo()`. In this case this turns out to be (10 types implementing `Trait`)\*(3
 types being fed to `foo()`) = 30 implementations!
 
 With real world traits these numbers can grow drastically.