In order to have a protocol called Catchable we need to conform a GenericNode to Catchable multiple times: once for if it is a Result and once for if it is a Promise. But this is not allowed. The alternatives: make subclasses rather than have everything be typealias, or have the body of `catch` switch on the type of When

Looks like we are forced into a tradeoff of two options:
1) Mark all catch bodies as `@escaping` and lose some compiler efficiency
2) Have the catchable protocol require not `catch` methods, but `catchAsync` and `catchSyncEscaping` or something like that

…protocols depending on different `where` conditions

… hood. Darn

…implement thenable

…com/async-plus/async-plus into keep-type-flags-operation-protocols

… values