all: Refactor to non-global logger

Note that this looks like overkill for just the logger, and that is correct,
but this will make sense once we start with the template handling etc.

Updates #2701

hugolib/rss_test.go

@@ -32,7 +32,7 @@ func TestRSSOutput(t *testing.T) {
 		writeSource(t, filepath.Join("content", "sect", s.Name), string(s.Content))
 	}
 
-	if err := buildAndRenderSite(newSiteDefaultLang()); err != nil {
+	if err := buildAndRenderSite(NewSiteDefaultLang()); err != nil {
 		t.Fatalf("Failed to build site: %s", err)
 	}