Better support for BLOBs

- Limbo command line shell supports e.g. `SELECT x'616263';`
- `EXPLAIN SELECT x'616263';` lists the opcode

Missing:

- Command line shell not entirely compatible with SQLite when blobs have
  non-printable characters in the middle (e.g. `SELECT x'610062';`)
- Python bindings not supported (incoming soon)

testing/scalar-functions.test

@@ -395,14 +395,13 @@ do_execsql_test typeof-real {
   SELECT typeof(1.0);
 } {real}
 
-# TODO: Uncomment when blobs are better supported
-# do_execsql_test typeof-blob {
-#   SELECT typeof(x'61');
-# } {blob}
-#
-# do_execsql_test typeof-blob-empty {
-#   SELECT typeof(x'');
-# } {blob}
+do_execsql_test typeof-blob {
+  SELECT typeof(x'61');
+} {blob}
+
+do_execsql_test typeof-blob-empty {
+  SELECT typeof(x'');
+} {blob}
 
 do_execsql_test typeof-sum-integer {
   SELECT typeof(sum(age)) from users;