Support hyphenated attribute names.

`Browser.Find()` doesn't support finding elements by attributes with names contains a hyphens.

Fore example, you might want to select a meta-refresh tag such as

    <meta http-equiv="refresh" content="5;URL='http://example.com/'">

or an input with a `data-` attribute

    <input type="text" data-foo="bar" />

C# doesn't support hyphens in property names on anonymous types, e.g. `new { data-foo = "bar" }` will not compile. My suggestion is to check if a property has an underscore in it's name. If it does, and the initial call to `FilterElementsByAttributeName` returns no elements, replace the underscore with a hyphen and try again.