Docs/higher kinded v2

Adds the higher-kinded schema to the docs.

Review by @DarkDimius @samuelgruetter 
I just realized you need these `self` names right after, for doing the reduction without shadowing. But still, it's not like the expansion is different for no reason.
I'd add:

```diff
 These expand as follows:

+    type RMap  = Lambda2 { type Apply = Map[Arg2, Arg1] }
+    type RRMap = Lambda2 { type Apply = RMap[Arg2, Arg1] }

+which are equivalent to:
+
     type RMap  = Lambda2 { self1 => type Apply = Map[self1.Arg2, self1.Arg1] }
     type RRMap = Lambda2 { self2 => type Apply = RMap[self2.Arg2, self2.Arg1] }
+We'll need these names to show how these aliases expand.
```
(Maybe that's too much clarity, but I'm just trying to make sure I understand this, and making it clearer as a side effect.)