add sql builder doc

public/help/action/sql-builder.md

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+
+## SQL-Builder
+
+Through the SQL-Buider you can build a response based on multiple SQL queries.
+You can use a specialised JSON format to specify the SQL queries and the 
+response format.
+
+### Elements
+
+#### Collection
+
+All elements which contain an `!collection` key are replaced with an array. The
+array contains for each result an object in the format of the definition.
+
+    {
+        "!collection": "SELECT id, title, content, date FROM app_news ORDER BY id DESC",
+        "definition": {
+            "displayTitle": "title",
+            "createDate": "date|datetime",
+        }
+    }
+
+#### Entity
+
+All elements which contain an `!entity` key are replaced with an object. The
+object has the format of the definition.
+
+    {
+        "!entity": "SELECT id, name, date FROM app_author WHERE id = :authorId"
+        "parameters": {"authorId": "$authorId"},
+        "definition": {
+            "displayName": "name",
+            "insertDate": "date|datetime"
+        }
+    }
+
+#### Value
+
+All elements which contain an `!value` key are replaced with a single value.
+
+    {
+        "!value": "SELECT COUNT(*) FROM app_news"
+    }
+
+### Example
+
+    {
+        "totalResults": {
+            "!value": "SELECT COUNT(*) FROM app_news"
+        },
+        "entry": {
+            "!collection": "SELECT id, title, content, date FROM app_news ORDER BY id DESC",
+            "definition": {
+                "id": "id|integer",
+                "title": "title",
+                "date": "date|datetime"
+            }
+        }
+    }
+
+
+