Do not use custom UEvent.String() that produces human-unreadable representation

[anatol]

The output of struct's String() suppose to be consumed as a formatted text primarily by a human. With something like this fmt.Printf("%+v", event).

Unfortunately current String() has a number of problems:

• it uses non-standard struct representation that is inconsistent with the majority of the golang libraries/projects
• it contacts the fields
• %+v does not print fields names
• Printf() does not print Env, probably because the current string prints NUL-symbol (it is a bad idea to use NUL-symbol).

Please remove the custom incorrect String() implementation and consider using the default implementation.