Register option without prefix

- While option should be defined i.e. using "--arg", discover
  prefix from ShellMethod#prefix and use that if just "arg"
  is defined.
- Backport #575
- Fixes #577

spring-shell-docs/src/main/asciidoc/using-shell-options-definition.adoc

@@ -25,6 +25,16 @@ include::{snippets}/OptionSnippets.java[tag=option-with-annotation]
 ----
 ====
 
+If option name is defined without prefix, either `-` or `--`, it is discovered
+from _ShellMethod#prefix_.
+
+====
+[source, java, indent=0]
+----
+include::{snippets}/OptionSnippets.java[tag=option-with-annotation-without-prefix]
+----
+====
+
 Programmatic way with `CommandRegistration` is to use method adding a long name.
 
 ====

spring-shell-docs/src/test/java/org/springframework/shell/docs/OptionSnippets.java

@@ -23,12 +23,20 @@ public class OptionSnippets {
 
 	class Dump1 {
 		// tag::option-with-annotation[]
-		public String example(@ShellOption(value = { "argx" }) String arg1) {
+		public String example(@ShellOption(value = { "--argx" }) String arg1) {
 			return "Hello " + arg1;
 		}
 		// end::option-with-annotation[]
 	}
 
+	class Dump7 {
+		// tag::option-with-annotation-without-prefix[]
+		public String example(@ShellOption(value = { "argx" }) String arg1) {
+			return "Hello " + arg1;
+		}
+		// end::option-with-annotation-without-prefix[]
+	}
+
 	class Dump2 {
 		// tag::option-without-annotation[]
 		public String example(String arg1) {