Return non-zero exit code on error in batch mode (closes #12)

A return code of 1 signals a SchemaException, which is useful to detect syntax
or validation errors.

src/main/java/uk/ac/ed/pguaglia/real/runtime/CommandLineApp.java

@@ -450,14 +450,23 @@ public final class CommandLineApp {
 			} catch (SchemaException e) {
 				System.err.println(String.format("ERROR: In \"%s\": %s", e.getExpression(), e.getMessage()));
 				System.err.flush();
+				if (batch == true) {
+					System.exit(1);
+				}
 				continue mainLoop;
 			} catch (IllegalStateException e) {
 				System.err.println(String.format("ERROR: In \"%s\": %s", expr, e.getMessage()));
 				System.err.flush();
+				if (batch == true) {
+					System.exit(-1);
+				}
 				continue mainLoop;
 			} catch (Exception e) {
 				e.printStackTrace();
 				System.err.flush();
+				if (batch == true) {
+					System.exit(-1);
+				}
 				continue mainLoop;
 			}
 		} while (batch == false);