Fixes 1243 (select mode enhancements)

This pull request fixes issue #1243 and add various select mode enhancements

* Add support for `Ctrl` modifiers, e.g. `Ctrl+Shift+Left`
* Fix exclusive selection
* Add cut, copy, and paste in select mode ala `$VIMRUNTIME/mswin.vim` instead of inserting control characters
* Fix mode after deleting selection in select mode
* Add corresponding tests and enhance old tests