Add independent PageMapper for annotation driven parsing

[code4craft]

Now annotation mode is separate from basic PageProcessor, but the parsing mode is useful in some cases.

I will try to write a independent PageMapper for just parsing. It can be used in PageParser.process.

public class GithubRepoPageProcessor implements PageProcessor {

    private Site site = Site.me().setRetryTimes(3);

    private PageMapper<GithubRepo> githubRepoPageMapper = new PageMapper<GithubRepo>(GithubRepo.class);

    @Override
    public void process(Page page) {
        page.addTargetRequests(page.getHtml().links().regex("(https://github\\.com/\\w+/\\w+)").all());
        page.addTargetRequests(page.getHtml().links().regex("(https://github\\.com/\\w+)").all());
        GithubRepo githubRepo = githubRepoPageMapper.get(page);
        page.putField("repo",githubRepo);
    }

    @Override
    public Site getSite() {
        return site;
    }

    public static void main(String[] args) {
        Spider.create(new GithubRepoPageProcessor()).addUrl("https://github.com/code4craft").thread(5).run();
    }
}