Add trim/0, ltrim/0 and rtrim/0 that trims leading and trailing whitespace (#3056)

docs/content/manual/manual.yml

@@ -1772,6 +1772,25 @@ sections:
             input: '["fo", "foo", "barfoo", "foobar", "foob"]'
             output: ['["fo","","bar","foobar","foob"]']
 
+      - title: "`trim`, `ltrim`, `rtrim`"
+        body: |
+
+          `trim` trims both leading and trailing whitespace.
+
+          `ltrim` trims only leading (left side) whitespace.
+
+          `rtrim` trims only trailing (right side) whitespace.
+
+          Whitespace characters are the usual `" "`, `"\n"` `"\t"`, `"\r"`
+          and also all characters in the Unicode character database with the
+          whitespace property. Note that what considers whitespace might
+          change in the future.
+
+        examples:
+          - program: 'trim, ltrim, rtrim'
+            input: '" abc "'
+            output: ['"abc"', '"abc "', '" abc"']
+
       - title: "`explode`"
         body: |