dsl: add Squib.configure

I ended up adding this one on a whim, but it feels like a long time coming. We need cleaner support for Rakefiles, and this is a good step toward that I think.

docs/config.rst

@@ -47,7 +47,7 @@ prefix
 
 img_dir
   default: ``'.'``
-  
+
   For reading image file command (e.g. png and svg), read from this directory instead
 
 warn_ellipsize
@@ -111,6 +111,19 @@ For debugging/sanity purposes, if you want to make sure your configuration optio
     puts backend # prints 'memory' by default
   end
 
+These are read-only - you will not be able to change these.
+
+Squib.configure sets options programmatically
+---------------------------------------------
+
+You can also use :doc:`/dsl/configure` to override anything in the config file. Use it like this:
+
+.. literalinclude:: ../samples/project/Rakefile
+  :language: ruby
+  :linenos:
+
+
+See :doc:`/guides/getting-started/part_3_workflows` for how we put this to good use.
 
 Making Squib Verbose
 --------------------

docs/dsl/configure.rst

@@ -0,0 +1,18 @@
+Squib.configure
+---------------
+
+Prior to the construction of a Squib::Deck, set a global default that overrides what is specified `config.yml`.
+
+This is intended to be done prior to Squib::Deck.new, and is intended to be used inside of a Rakefile
+
+Options
+^^^^^^^
+
+All options that are specified in :doc:`/config`
+
+Exmaples
+^^^^^^^^
+
+.. literalinclude:: ../../samples/project/Rakefile
+  :language: ruby
+  :linenos: