Updates according to review

Author: m-mohr

proposals/text_position.json renamed to proposals/text_find.json

@@ -1,5 +1,5 @@
 {
-    "id": "text_position",
+    "id": "text_find",
     "summary": "First position of a text in another text",
     "description": "Checks where the text (also known as *string*) specified for `pattern` is positioned in the text specified for `data` for the first time. No-data values are passed through.",
     "categories": [
@@ -35,13 +35,13 @@
         }
     ],
     "returns": {
-        "description": "A value >= 0 that indicates the position of the text, `-1` if the text was not found.",
+        "description": "A value >= 0 that indicates the position of the text, `null` if the text was not found.",
         "schema": {
             "type": [
                 "integer",
                 "null"
             ],
-            "minimum": -1
+            "minimum": 0
         }
     },
     "examples": [
@@ -50,7 +50,7 @@
                 "data": "Lorem ipsum dolor sit amet",
                 "pattern": "openEO"
             },
-            "returns": -1
+            "returns": null
         },
         {
             "arguments": {
@@ -64,7 +64,7 @@
                 "data": "Lorem ipsum dolor sit amet",
                 "pattern": "Ipsum Dolor"
             },
-            "returns": -1
+            "returns": null
         },
         {
             "arguments": {