ENH: code simplification, improvements for reading dictionary variables

- Now accept '/' when reading variables without requiring
  a surrounding '{}'

- fix some degenerate parsing cases when the first character is
  already bad.

  Eg, $"abc" would have previously parsed as a <$"> variable, even
  although a double quote is not a valid variable character.

  Now emits a warning and parses as a '$' token and a string token.

tutorials/verificationAndValidation/turbulentInflow/system/sampling

@@ -20,7 +20,7 @@ fieldAverage1
     type                fieldAverage;
     libs                (fieldFunctionObjects);
     writeControl        writeTime;
-    timeStart           ${/timeStart};
+    timeStart           $/timeStart;
 
     fields
     (
@@ -39,7 +39,7 @@ inletSampling
     type                sets;
     libs                (sampling);
     writeControl        writeTime;
-    timeStart           ${/timeStart};
+    timeStart           $/timeStart;
 
     interpolationScheme cellPoint;
     setFormat           raw;