run now returns success count, intercepted output and an error message. Good for parsing. Fixes #428

docs/scarpet/api/Auxiliary.md

@@ -313,11 +313,15 @@ read_file('foo', 'shared_text')     => ['one', 'two', 'three', '', 'four', '', '
   
 ### `run(expr)`
 
-Runs a vanilla command from the string result of the `expr` and returns its success count
+Runs a vanilla command from the string result of the `expr` and returns a triple of success count, 
+intercepted list of output messages, and error message if the command resulted in a failure. 
+Successful commands return `null` as their error.
 
 <pre>
-run('fill 1 1 1 10 10 10 air') -> 123 // 123 block were filled, this operation was successful 123 times out of a possible 1000 block volume
-run('give @s stone 4') -> 1 // this operation was successful once
+run('fill 1 1 1 10 10 10 air') -> [123, ["Successfully filled 123 blocks"], null] // 123 block were filled, this operation was successful 123 times out of a possible 1000 block volume
+run('give @s stone 4') -> [1, ["Gave 4 [Stone] to gnembon"], null] // this operation was successful once
+run('seed') -> [-170661413, ["Seed: [4031384495743822299]"], null]
+run('sed') -> [0, [], "sed<--[HERE]"] // wrong command
 </pre>
 
 ### `save()`