Add a convenience case for string arrays in HTML attributes

[wilzbach]

- auto myClasses = ["foo", "bar"];
div(class="#{myClasses}")

should yield:

<div class="foo bar" />

See also: dlang/ddox#171

[schveiguy]

I imagine you can define a type Classes that takes care of this, no? Then it becomes:

- auto myClasses = Classes("foo", "bar");
div(class="#{myClasses}")