Move site files to site/ subdirectory

It's rather messy otherwise, and in particular the `**/*.markdown`
rule matches `.markdown` files belonging to the source of dependent
packages in in the dist-newstyle directory.

builder/site.hs

@@ -16,7 +16,7 @@ import           Testimonial
 
 --------------------------------------------------------------------------------
 main :: IO ()
-main = mkContext >>= \ctx -> hakyll $ do
+main = mkContext >>= \ctx -> hakyllWith configuration $ do
   match "testimonials/logos/*" $ do
     route idRoute
     compile copyFileCompiler
@@ -65,6 +65,9 @@ main = mkContext >>= \ctx -> hakyll $ do
     compile templateCompiler
 
 
+configuration :: Configuration
+configuration = defaultConfiguration{ providerDirectory = "site" }
+
 parseTestimonialCompiler :: Compiler (Item Testimonial)
 parseTestimonialCompiler = do
   identifier  <- getUnderlying