Improve error message for issue #618

[ratmice]

This should fix #618 which is a similar CTParserBuilder error that lacked span information (or a good error).

Tested with the calc_parsetree example with the following diff applied

diff --git a/lrpar/examples/calc_parsetree/src/calc.y b/lrpar/examples/calc_parsetree/src/calc.y
index b8a1f34d..25b165ec 100644
--- a/lrpar/examples/calc_parsetree/src/calc.y
+++ b/lrpar/examples/calc_parsetree/src/calc.y
@@ -1,5 +1,5 @@
 %grmtools{
-    yacckind: Original(GenericParseTree),
+    yacckind: Original(UserAction),
     test_files: ["input*.txt"],
 }
 %start Expr

--- stderr
  thread 'main' (2467488) panicked at lrpar/examples/calc_parsetree/build.rs:16:10:
  called `Result::unwrap()` on an `Err` value:
  8| Expr: Expr '+' Term
     ^^^^ Rule missing action type
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[ratmice]

Oops, one thing I am just noticing is that this doesn't have filename information.

[ltratt]

Please squash.

[ratmice]

Squashed