Revamp the config system for Top/Harness (#347)

* Refactor how Configs parameterize the Top and TestHarnesses

* Bump sha3, testchipip, icenet, firesim

docs/Customization/Custom-Chisel.rst

@@ -0,0 +1,59 @@
+.. _custom_chisel:
+
+Integrating Custom Chisel Projects into the Generator Build System
+==================================================================
+
+.. warning::
+   This section assumes integration of custom Chisel through git submodules.
+   While it is possible to directly commit custom Chisel into the Chipyard framework,
+   we heavily recommend managing custom code through git submodules. Using submodules decouples
+   development of custom features from development on the Chipyard framework.
+
+
+While developing, you want to include Chisel code in a submodule so that it can be shared by different projects.
+To add a submodule to the Chipyard framework, make sure that your project is organized as follows.
+
+.. code-block:: none
+
+    yourproject/
+        build.sbt
+        src/main/scala/
+            YourFile.scala
+
+Put this in a git repository and make it accessible.
+Then add it as a submodule to under the following directory hierarchy: ``generators/yourproject``.
+
+The ``build.sbt`` is a minimal file which describes metadata for a Chisel project.
+For a simple project, the ``build.sbt`` can even be empty, but below we provide an example
+build.sbt.
+
+.. code-block:: scala
+
+    organization := "edu.berkeley.cs"
+
+    version := "1.0"
+
+    name := "yourproject"
+
+    scalaVersion := "2.12.4"
+
+
+
+.. code-block:: shell
+
+    cd generators/
+    git submodule add https://git-repository.com/yourproject.git
+
+Then add ``yourproject`` to the Chipyard top-level build.sbt file.
+
+.. code-block:: scala
+
+    lazy val yourproject = (project in file("generators/yourproject")).settings(commonSettings).dependsOn(rocketchip)
+
+You can then import the classes defined in the submodule in a new project if
+you add it as a dependency. For instance, if you want to use this code in
+the ``example`` project, change the final line in build.sbt to the following.
+
+.. code-block:: scala
+
+    lazy val example = (project in file(".")).settings(commonSettings).dependsOn(testchipip, yourproject)