IE8 issues

[agentcooper]

Following stuff fails in IE8:

• IMG tag
• style attribute
• data-attributes are not saved: there is no dataset

[marcelklehr]

• IMG tag
• style attribute (see 19a4d0f)
• data-attributes (see 7c5846b)

[marcelklehr]

(I'm splitting up your pull request into smaller chunks)

[niksy]

It seems like IE8 needs polyfills for specific features:

• Array.prototype.forEach
• Array.prototype.reduce
• Array.prototype.slice on host objects

These can be applied via shims like "es5-shim" or using ponyfills. I don’t know if this is really necessary but it can make it easier to make vdom-virtualize to work with older environments.