Added support and test for style attributes that are strings instead …

[virtualpatterns]

…of objects.

virtual-dom/h accepts style attributes that are strings, not objects. When the results are passed into vdom-to-html it doesn't render style attributes that are strings well.

[coveralls]

Coverage remained the same at 100.0% when pulling 632d759 on virtualpatterns:master into 6999583 on nthtran:master.

[rusintez]

👍 could help dramatically, my -webkit- prefixes are rendering as webkit, with this should go away if i'll stringify them myself.