Composer fixes and improvements (#259)

* 3.x-dev
* Use new composer constraints notation

composer.json

@@ -17,28 +17,28 @@
         }
     ],
     "require": {
-        "symfony/http-kernel": "~2.3|~3.0",
-        "symfony/form": "~2.3|~3.0",
-        "doctrine/common": "~2.3",
-        "sonata-project/core-bundle": "~2.3,>=2.3.10",
-        "sonata-project/cache": "~1.0"
+        "symfony/http-kernel": "^2.3 || ^3.0",
+        "symfony/form": "^2.3 || ^3.0",
+        "doctrine/common": "^2.3",
+        "sonata-project/core-bundle": "3.x-dev@dev",
+        "sonata-project/cache": "^1.0"
     },
     "require-dev": {
-        "knplabs/knp-menu-bundle": "~2.0|~2.1@dev",
-        "sonata-project/admin-bundle": "dev-master",
-        "symfony/phpunit-bridge": "~2.7|~3.0"
+        "knplabs/knp-menu-bundle": "^2.0 || ^2.1@dev",
+        "sonata-project/admin-bundle": "3.x-dev@dev",
+        "symfony/phpunit-bridge": "^2.7 || ^3.0"
     },
     "suggest": {
-        "knplabs/knp-menu-bundle": "~2.0",
-        "sonata-project/cache-bundle": "~2.1"
+        "knplabs/knp-menu-bundle": "^2.0",
+        "sonata-project/cache-bundle": "^3.0"
     },
     "autoload": {
         "psr-4": { "Sonata\\BlockBundle\\": "" },
         "files": ["Resources/stubs/symfony2.php"]
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.4.x-dev"
+            "dev-master": "3.x-dev"
         }
     }
 }