Add Scaladoc for basic usage of gpu and cpu

Author: Atry

cpu/build.sbt

@@ -1 +1,24 @@
 enablePlugins(Example)
+
+import scala.meta._
+exampleSuperTypes := exampleSuperTypes.value.map {
+  case ctor"_root_.org.scalatest.FreeSpec" =>
+    ctor"_root_.org.scalatest.AsyncFreeSpec"
+  case otherTrait =>
+    otherTrait
+}
+
+libraryDependencies += ("org.lwjgl" % "lwjgl" % "3.1.6" % Test).jar().classifier {
+  import scala.util.Properties._
+  if (isMac) {
+    "natives-macos"
+  } else if (isLinux) {
+    "natives-linux"
+  } else if (isWin) {
+    "natives-windows"
+  } else {
+    throw new MessageOnlyException(s"lwjgl does not support $osName")
+  }
+}
+
+fork := true

cpu/src/main/scala/com/thoughtworks/compute/cpu.scala

@@ -4,6 +4,24 @@ import com.thoughtworks.feature.Factory
 import com.typesafe.scalalogging.StrictLogging
 import org.lwjgl.opencl.CL10.CL_DEVICE_TYPE_CPU
 
+/** Contains N-dimensional array types on GPU.
+  *
+  * You may want to import [[Tensor]], which is the base type of N-dimensional arrays:
+  *
+  * {{{
+  * import com.thoughtworks.compute.cpu.Tensor
+  * }}}
+  *
+  * @example In Compute.scala, an N-dimensional array is typed as [[Tensor]],
+  *          which can be created from [[scala.collection.Seq]] or [[scala.Array]].
+  *
+  *          {{{
+  *          val my2DArray: Tensor = Tensor(Array(Seq(1.0f, 2.0f), Seq(3.0f, 4.0f)))
+  *
+  *          my2DArray.toString should be("[[1.0,2.0],[3.0,4.0]]")
+  *          }}}
+  *
+  */
 object cpu
     extends StrictLogging
     with Tensors.UnsafeMathOptimizations

gpu/src/main/scala/com/thoughtworks/compute/gpu.scala

@@ -1,9 +1,17 @@
 package com.thoughtworks.compute
 
-import com.thoughtworks.feature.Factory
 import com.typesafe.scalalogging.StrictLogging
-import org.lwjgl.opencl.CL10.CL_DEVICE_TYPE_CPU
 
+/** Contains N-dimensional array types on CPU.
+  *
+  * All the usage of this [[gpu]] object is same as [[cpu]], except the `import` statement:
+  *
+  * {{{
+  * import com.thoughtworks.compute.gpu._
+  * }}}
+  *
+  * @see [[cpu]] for Usage.
+  */
 object gpu
     extends StrictLogging
     with Tensors.UnsafeMathOptimizations