Replace Makefile with GruntJS

A rebase (against soon-to-be 3.0.0-rc.1) & squash of
https://github.com/twbs/bootstrap/pull/7786 AKA
https://github.com/twitter/bootstrap/pull/7786
originally by
@seriema
@mokkabonna
@jojohess

Rebased by @cvrebert

package.json

@@ -5,7 +5,7 @@
   , "keywords": ["bootstrap", "css"]
   , "homepage": "http://twbs.github.com/bootstrap/"
   , "author": "Twitter Inc."
-  , "scripts": { "test": "make test" }
+  , "scripts": { "test": "grunt test" }
   , "repository": {
       "type": "git"
     , "url": "https://github.com/twbs/bootstrap.git"
@@ -17,9 +17,14 @@
     }
   ]
   , "devDependencies": {
-      "uglify-js": "1.3.4"
-    , "jshint": "2.1.2"
-    , "recess": "1.1.7"
-    , "connect": "2.1.3"
+      "grunt": "~0.4.1"
+    , "grunt-contrib-connect": "~0.3.0"
+    , "grunt-contrib-clean": "~0.5.0"
+    , "grunt-contrib-concat": "~0.3.0"
+    , "grunt-contrib-jshint": "~0.6.0"
+    , "grunt-contrib-uglify": "~0.2.2"
+    , "grunt-contrib-qunit": "~0.2.2"
+    , "grunt-contrib-watch": "~0.5.1"
+    , "grunt-recess": "~0.3.3"
   }
 }