* This adds an option to the IDEA plugin (checkbox) to format JavaDoc comments.
  It is disabled by default.
* As the IDEA plugin (sometimes) uses the bootstrapping formatter service, which in turn
  uses the command line tool, this also add an option `--format-javadoc` to
  the command line tool.
* To pass the options to the FormatterService loaded via service provider, I added a
  method `withOptions` to the service provided interface, which returns a new (immutable)
  instance with the updated options. Compared with the suggestion from the issue comment
  (palantir#724 (comment)),
  this (a) does not require deprecating methods and (b) the options can be set independently
  of where the formatter is actually used.
* Since the infrastructure to pass options to the formatter now exists, we could also
  add more options to the code style select configuration in the IDEA plugin, but I'm
  not sure if that makes sense (I want to use Palantir, after all).
* The issue also mentioned API compatibility. The service provider interface is compatible,
  most other classes and methods are internal. But if somebody more familar with the code
  base could take another look, that would be great.
* I also added a few tests for the new option.

…-javadoc

…-javadoc