re-add nam uses definition

to me this reads like we're renaming definitions to colliding names that
have been imported.

  use List/{length}

  length = 123

is parsed as

  List/length = 123

i do not understand how this is sensible, nor how this breaks when
removed.

src/book/parse.rs

@@ -65,6 +65,8 @@ impl<'i> KindParser<'i> {
     // Top level definition
     self.skip_trivia();
     let nam = self.parse_name()?;
+    // FIXME: this breaks definitions of terms with a name equivalent to one that has been imported.
+    let nam = uses.get(&nam).unwrap_or(&nam).to_string();
     self.skip_trivia();
 
     // Arguments (optional)