Symbol names with <impl> are too obscure

[bluss]

Symbol names of methods don't include the type name, instead they use the string <impl>.

Obscure symbol names makes reading backtraces, profiling and debugging harder.

Examples:

• _$LT$impl$GT$::with_capacity::h1e508e0577f260f2tka for Vec::with_capacity.
• isomorphism::_$LT$impl$GT$::new::new::h10192896492405891948
  for an item named isomorphism::Vf2State::new; with the type name gone, it's
  hard to directly understand which method it is

[gwillen]

Yay! Thank you. :D This was really annoying.