Mention `HAIR` to clarify

src/mir/construction.md

@@ -14,6 +14,7 @@ list of items:
 The lowering is triggered by calling the [`mir_built`] query.
 There is an intermediate representation
 between [HIR] and [MIR] called the [THIR] that is only used during the lowering.
+[THIR] means "Typed HIR" and used to be called "HAIR (High-level Abstract IR)".
 The [THIR]'s most important feature is that the various adjustments (which happen
 without explicit syntax) like coercions, autoderef, autoref and overloaded method
 calls have become explicit casts, deref operations, reference expressions or

src/overview.md

@@ -187,10 +187,10 @@ for different purposes:
 - High-level IR (HIR): This is a sort of desugared AST. It's still close
   to what the user wrote syntactically, but it includes some implicit things
   such as some elided lifetimes, etc. This IR is amenable to type checking.
-- Typed HIR (THIR): This is an intermediate between HIR and MIR. It is like the HIR
-  but it is fully typed and a bit more desugared (e.g. method calls and implicit
-  dereferences are made fully explicit). Moreover, it is easier to lower to MIR
-  from THIR than from HIR.
+- Typed HIR (THIR): This is an intermediate between HIR and MIR, and used to be called
+  High-level Abstract IR (HAIR). It is like the HIR but it is fully typed and a bit
+  more desugared (e.g. method calls and implicit dereferences are made fully explicit).
+  Moreover, it is easier to lower to MIR from THIR than from HIR.
 - Middle-level IR (MIR): This IR is basically a Control-Flow Graph (CFG). A CFG
   is a type of diagram that shows the basic blocks of a program and how control
   flow can go between them. Likewise, MIR also has a bunch of basic blocks with