Deprecate some non-standard and obsolete types and fields.

See:
* https://developer.mozilla.org/en-US/docs/Web/HTML/Element/bgsound
* https://msdn.microsoft.com/en-us/library/windows/apps/hh965347.aspx
* https://developer.mozilla.org/en-US/docs/Web/API/window/setImmediate
* https://developer.mozilla.org/en-US/docs/Web/API/Window/clearImmediate
* https://developer.mozilla.org/en/docs/Web/API/Event/srcElement
* https://msdn.microsoft.com/en-us/library/hh869721(v=vs.85).aspx
* https://www.w3.org/TR/html5/obsolete.html
* https://developer.mozilla.org/en-US/docs/Web/API/HTMLFontElement

Author: danielnixon

build.sbt

@@ -11,7 +11,7 @@ scalaVersion in ThisBuild := crossScalaVersions.value.head
 val commonSettings = Seq(
   version := "0.9.2-SNAPSHOT",
   organization := "org.scala-js",
-  scalacOptions ++= Seq("-deprecation", "-feature", "-Xfatal-warnings")
+  scalacOptions ++= Seq("-deprecation", "-feature")
 )
 
 normalizedName := "scalajs-dom"

src/main/scala/org/scalajs/dom/raw/Html.scala

@@ -798,6 +798,7 @@ abstract class HTMLBaseElement extends HTMLElement {
 }
 
 @js.native
+@deprecated("Obsolete.", "HTML 3.2")
 trait HTMLNextIdElement extends HTMLElement {
   var n: String = js.native
 }
@@ -830,6 +831,7 @@ trait HTMLAreasCollection extends HTMLCollection {
 }
 
 @js.native
+@deprecated("Obsolete.", "HTML 5")
 abstract class HTMLAppletElement extends HTMLElement {
   var width: Double = js.native
   var codeType: String = js.native
@@ -1143,6 +1145,7 @@ abstract class HTMLLinkElement extends HTMLElement with LinkStyle {
 }
 
 @js.native
+@deprecated("Obsolete.", "HTML 4.01")
 abstract class HTMLFontElement extends HTMLElement {
   var face: String = js.native
 }
@@ -3719,6 +3722,7 @@ abstract class HTMLFieldSetElement extends HTMLElement {
 }
 
 @js.native
+@deprecated("Non standard.", "forever")
 abstract class HTMLBGSoundElement extends HTMLElement {
   var balance: js.Any = js.native
   var volume: js.Any = js.native
@@ -4232,6 +4236,7 @@ abstract class HTMLOptGroupElement extends HTMLElement {
  * MDN
  */
 @js.native
+@deprecated("Obsolete.", "HTML 4.01")
 abstract class HTMLIsIndexElement extends HTMLElement {
 
   /**
@@ -4378,6 +4383,7 @@ abstract class HTMLTrackElement extends HTMLElement {
 }
 
 @js.native
+@deprecated("Obsolete.", "HTML 5")
 abstract class HTMLMarqueeElement extends HTMLElement {
   var width: String = js.native
   var onbounce: js.Function1[Event, _] = js.native

src/main/scala/org/scalajs/dom/raw/lib.scala

@@ -5344,6 +5344,7 @@ class Event extends js.Object {
 
   def `type`: String = js.native
 
+  @deprecated("Non standard.", "forever")
   def srcElement: Element = js.native
 
   /**
@@ -6688,8 +6689,10 @@ trait AudioTrackList extends EventTarget with DOMList[AudioTrack] {
 
 @js.native
 trait WindowTimersExtension extends js.Object {
+  @deprecated("Non standard.", "forever")
   def clearImmediate(handle: Int): Unit = js.native
 
+  @deprecated("Non standard.", "forever")
   def setImmediate(handler: js.Function0[Any]): Int = js.native
 }