The documentation for the plugin is contained in GitHub wiki pages.
The option needed not include a preview is called usePreview
(ref); set it to false
(demo):
To autoaccept the contents, set the autoAccept
option to true
$('#keyboard').keyboard({
layout: 'qwerty',
// true: preview added above keyboard;
// false: original input/textarea used
usePreview: false
// Auto-accept content when clicking outside the
// keyboard (popup will close)
autoAccept: true
});