Support for Y in visual mode, indent fixes

This pull contains 2 commits, for separate issues in visual mode:

 * The second commit adds support for Y in visual mode, [Issue 317](https://github.com/JugglerShu/XVim/issues/317)

 * The earlier commit removes logic that was adding extra newlines when putting (`p`) in visual mode. I'm not sure why this code was added, but the extra newlines were triggering Xcode's autoindent behavior and causing formatting problems. Removing this code fixed those issues.