Use thiserror for error handling with less boilerplate

src/datamatrix/encoder/x12_encoder.rs

@@ -82,7 +82,7 @@ impl X12Encoder {
         context.updateSymbolInfo();
         let available = context
             .getSymbolInfo()
-            .ok_or(Exceptions::illegalState)?
+            .ok_or(Exceptions::ILLEGAL_STATE)?
             .getDataCapacity()
             - context.getCodewordCount() as u32;
         let count = buffer.chars().count();