Use the term "EBB parameter" everywhere.

Add EBB parameter and EBB argument to the langref glossary to clarify
the distinction between formal EBB parameter values and arguments passed
to branches.

- Replace "ebb_arg" with "ebb_param" in function names that deal with
  EBB parameters.
- Rename the ValueDef variants to Result and Param.
- A bunch of other small langref fixes.

No functional changes intended.

lib/cretonne/src/ir/progpoint.rs

@@ -35,8 +35,8 @@ impl From<Ebb> for ProgramPoint {
 impl From<ValueDef> for ProgramPoint {
     fn from(def: ValueDef) -> ProgramPoint {
         match def {
-            ValueDef::Res(inst, _) => inst.into(),
-            ValueDef::Arg(ebb, _) => ebb.into(),
+            ValueDef::Result(inst, _) => inst.into(),
+            ValueDef::Param(ebb, _) => ebb.into(),
         }
     }
 }
@@ -66,8 +66,8 @@ impl From<Ebb> for ExpandedProgramPoint {
 impl From<ValueDef> for ExpandedProgramPoint {
     fn from(def: ValueDef) -> ExpandedProgramPoint {
         match def {
-            ValueDef::Res(inst, _) => inst.into(),
-            ValueDef::Arg(ebb, _) => ebb.into(),
+            ValueDef::Result(inst, _) => inst.into(),
+            ValueDef::Param(ebb, _) => ebb.into(),
         }
     }
 }