blogex: CRAP scores as a Lens sensor (ex_crap)

Same wiring as app: `crap` reads the export from `test.coverage`, runs in
MIX_ENV=test, and refuses to score when the export is absent.

Baseline at the default threshold (30): 12 files, 59 functions, worst score
6.00. Nothing to fix; blogex's CRAP ceiling is its coverage ceiling, which the
behavior-test yaks already own.

blogex/mix.exs

@@ -46,7 +46,8 @@ defmodule Blogex.MixProject do
       {:jason, "~> 1.4"},
       {:plug, "~> 1.15"},
       {:ex_doc, "~> 0.34", only: :dev, runtime: false},
-      {:rustler, "~> 0.38.0", optional: true}
+      {:rustler, "~> 0.38.0", optional: true},
+      {:ex_crap, "~> 0.1.1", only: [:dev, :test], runtime: false}
     ]
   end