Rework command parser

- Previously CommandParser contained parser which was
  scannerless type of brute force parsing of command
  line args.
- Contract in that old parser wasn't super clear what
  is its role with caller as it was given options
  and registration was parsed in a Shell class.
- Add completely new parser package which has better
  model and which will be much easier to modify for
  future needs.
- Change some interfaces around parsing so that we do
  as much in this new parsing model instead of pre-parsing
  something in a Shell class.
- We also try to move away from using exceptions as
  a message delivery which had its own problems. Instead
  introducing parser messages which gives better info
  when errors are detected.
- Add ParserConfig class which allows to expose settings
  to change some parser features. Later this will be
  exposed to user so that some features can be turned on/off
  for an actual shell needs.
- Fixes #646

spring-shell-standard/src/main/java/org/springframework/shell/standard/StandardMethodTargetRegistrar.java

@@ -162,9 +162,6 @@ public class StandardMethodTargetRegistrar implements MethodTargetRegistrar {
 								else if (ClassUtils.isAssignable(Boolean.class, parameterType)) {
 									optionSpec.arity(OptionArity.ZERO);
 								}
-								else {
-									optionSpec.arity(OptionArity.EXACTLY_ONE);
-								}
 							}
 							if (!ObjectUtils.nullSafeEquals(so.defaultValue(), ShellOption.NONE)
 									&& !ObjectUtils.nullSafeEquals(so.defaultValue(), ShellOption.NULL)) {