Allow reusing InlineWrapDirective for other element types (#186)

* Allow reusing InlineWrapDirective for other element types

For example you could add an `InlineWrapDirective("aside")` to allow
`@aside[text] { .blue }` leading to `<aside class="blue">text</aside>".

* Also allow the uppercase variant

And avoid types getting confused somehow

core/src/main/scala/com/lightbend/paradox/markdown/Directive.scala

@@ -501,7 +501,8 @@ case class WrapDirective(typ: String) extends ContainerBlockDirective(Array(typ,
  *
  * Wraps inner contents in a `span`, optionally with custom `id` and/or `class` attributes.
  */
-case class InlineWrapDirective(typ: String) extends InlineDirective("span") {
+case class InlineWrapDirective(typ: String) extends InlineDirective(Array(typ, typ.toUpperCase): _*) {
+
   def render(node: DirectiveNode, visitor: Visitor, printer: Printer): Unit = {
     val id =
       node.attributes.identifier match {