Moved the pull to refresh to a separate subclass

[ipodishima]

The idea behind is to be able to provide some subclass for the refresh view. That way you can get rid of the old fashioned arrow while continuing to use this great implementation for pull to refresh

[self.tableView addPullToRefresh:[SVDemoPullToRefresh class] withActionHandler:^{
    [weakSelf insertRowAtTop];
}];

[shouze]

:+1:

[LawrenceHan]

Hi I created a pull request in https://github.com/LawrenceHan/SVPullToRefresh/pull/14

I will merge it after I tested it.

[LawrenceHan]

@ipodishima Hi, I have merged it.