Explicit model

[remkop]

For some JVM languages, Java annotations are not the most convenient way to express a command line configuration. In some cases, a builder-like API may be more useful.

The new picocli model should be flexible and powerful enough to be a base to create DSL on top of.

A stronger model is needed to support new features like #182 (annotated methods) and #144 (mixins).

Related to: #257 (parse results API), #260 (use builders or keep setter methods)

TODO:

• add printHelpIfRequested(ParseResult) method
• Add BaseParseResultHandler that prints help if requested and calls execute(ParseResult) otherwise

[remkop]

Todo:

• Validate positional parameters index before adding in add method
• In DSL, add getAt and setAt methods to support adding positional parameters with this syntax:

CliBuilder2 cli = ...
cli[0] = PositionalParamSpec.builder().build();
cli[1] = PositionalParamSpec.builder().build();
...