add getOption method (#92)

Author: SentryMan

prism-core/src/main/java/io/avaje/prism/internal/APContextWriter.java

@@ -322,6 +322,16 @@ public static void write(PrintWriter out, String packageName, boolean moduleRead
             + "    return getCtx().typeUtils;\n"
             + "  }\n"
             + "\n"
+            + "/**\n"
+            + "   * Returns processor-specific option passed to the annotation processing tool.\n"
+            + "   *\n"
+            + "   * @param key the key of the processor option\n"
+            + "   * @return an Optional for the processor option, or null if none is available.\n"
+            + "   * @see {@link ProcessingEnvironment#getOptions()}\n"
+            + "   */\n"
+            + "  public static Optional<String> getOption(String key) {\n"
+            + "    return Optional.ofNullable(processingEnv().getOptions().get(key));\n"
+            + "  }\n"
             + "  /**\n"
             + "   * Determine whether the first type can be assigned to the second\n"
             + "   *\n"