feat(tazjin/presentations): bootstrap tvix-eval-2023 presentation

I spent way too much time fighting LaTeX to do roughly what I want
here again, but all the alternatives are even worse.

Change-Id: Ibe12a4ce175ceb73e9d6e276613dcd4827dd76c4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9150
Autosubmit: tazjin <tazjin@tvl.su>
Reviewed-by: Mark Shevchenko <markshevchenko@gmail.com>
Tested-by: BuildkiteCI

users/tazjin/presentations/tvix-eval-2023/cppnix-example-lexer.cpp

@@ -0,0 +1,13 @@
+attrpath
+  : attrpath '.' attr {
+    $$ = $1; $1->push_back(AttrName(data->symbols.create($3)));
+  }
+  | attrpath '.' string_attr
+    { $$ = $1;
+      ExprString * str = dynamic_cast<ExprString *>($3);
+      if (str) {
+          $$->push_back(AttrName(data->symbols.create(str->s)));
+          delete str;
+      } else
+          $$->push_back(AttrName($3));
+    }