ngWigHtml directive suggestion

Hey man,
I've added a simple directive to allow ngWig binding to html. As for the $sce I think I pass that since your editor does not yet or not going to add any further css  customization. I made modification to the file in dist/ng-wig.js, dist/demo.html. the demo contain sample template how to assign the directive. As it is require angular-sanitize module loaded.

`<ng-wig-html to-bind="text2"></ng-wig-html>`

`text2` is the actual model assign in the ng-wig directive.