Composer improvements

* PHP requirements
* New constraint notations format
* New stable sonata packages
* Improve conflict section
* Remove minimum-stability rule
* Improve description

composer.json

@@ -1,7 +1,7 @@
 {
     "name": "sonata-project/page-bundle",
     "type": "symfony-bundle",
-    "description": "Symfony SonataPageBundle",
+    "description": "This bundle provides a Site and Page management through container and block services",
     "keywords": ["page", "sonata", "cms"],
     "homepage": "https://sonata-project.org/bundles/page",
     "license": "MIT",
@@ -17,34 +17,34 @@
         }
     ],
     "require": {
-        "symfony/symfony": "~2.3|~3.0",
-        "sonata-project/admin-bundle": "~2.4",
-        "sonata-project/block-bundle": "~2.3",
-        "sonata-project/seo-bundle": "~2.0",
-        "sonata-project/doctrine-extensions" : "~1.0",
+        "php": "^5.3 || ^7.0",
+        "symfony/symfony": "^2.3 || ^3.0",
+        "sonata-project/admin-bundle": "^3.0",
+        "sonata-project/block-bundle": "^3.0",
+        "sonata-project/seo-bundle": "^2.0",
+        "sonata-project/doctrine-extensions" : "^1.0",
         "sonata-project/cache-bundle": "^2.1.7",
         "sonata-project/cache": "^1.0.2",
-        "sonata-project/core-bundle": "^2.3.1",
-        "symfony-cmf/routing-bundle": "~1.1",
-        "sonata-project/notification-bundle": "~2.2",
-        "sonata-project/datagrid-bundle": "~2.2",
-        "cocur/slugify": "~1.0"
+        "sonata-project/core-bundle": "^3.0",
+        "symfony-cmf/routing-bundle": "^1.1",
+        "sonata-project/notification-bundle": "^3.0",
+        "sonata-project/datagrid-bundle": "^2.2",
+        "cocur/slugify": "^1.0"
     },
     "require-dev": {
-        "sonata-project/doctrine-orm-admin-bundle": "~2.2",
-        "symfony/phpunit-bridge": "~2.7|~3.0",
-        "friendsofsymfony/rest-bundle": "~1.1",
-        "jms/serializer-bundle": "~0.11|~1.0",
-        "nelmio/api-doc-bundle": "~2.4"
+        "sonata-project/doctrine-orm-admin-bundle": "^3.0",
+        "symfony/phpunit-bridge": "^2.7 || ^3.0",
+        "friendsofsymfony/rest-bundle": "^1.1",
+        "jms/serializer-bundle": "^0.13 || ^1.0",
+        "nelmio/api-doc-bundle": "^2.4"
     },
     "conflict": {
-        "jms/serializer": "<0.13"
+        "jms/serializer": "<0.13",
+        "sonata-project/doctrine-orm-admin-bundle": "<3.0 || >=4.0"
     },
     "suggest": {
-        "sonata-project/doctrine-orm-admin-bundle": "~2.2"
+        "sonata-project/doctrine-orm-admin-bundle": "^2.2"
     },
-    "minimum-stability": "dev",
-    "prefer-stable": true,
     "autoload": {
         "psr-4": { "Sonata\\PageBundle\\": "" }
     },