CopyOnWrite ArrayList/Slice

[vkuzmin-uber]

Java 5 introduced:

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/CopyOnWriteArrayList.html

It's very efficient if you have a List where you mostly need to iterate the ArrayList and don't modify it too often.

I used this data structure at Java and have an idea how to make it right at Go. I am willing to work on it and create a Pull request then. Just want to make sure there is no active development or it was discussed and rejected by some reason.