ComboExtractor support for annotation.

Request priority support (using PriorityScheduler).

Complete some I18n work (comments and documents).

More convenient extractor API:

• Add attribute name select for CSSSelector.

• Group of regex selector can be specified.

• Add OrSelector.

• Add Selectors, import static Selectors.* for fluent API such as:

  or(regex("<title>(.*)</title>"), xpath("//title"), $("title")).select(s);
  

• Add JsonPathSelector for Json parse.