Add newcomer label to issues

[tomcashman]

It would be good for newcomers who want to help ooc/rock to be able to find issues that are easy enough to fix and would help them become familiar with the rock codebase. So I think tagging suitable issues as 'newcomer' would be good. Are they any suitable issues at the moment?

[alexnask]

It is actually pretty tricky to say if an issue is going to be easy for a newcomer or not because of the nature of the problem.

Even what appears to be a trivial bug can be caused by a bizarre set of reasons.
I would actually say that adding features is easier than solving most bugs, if you keep a couple of things in mind (avoid double evaluation, replace nodes only when/if needed, use common roots for type inference).

I would say #985 and #992 should be fairly simple at the moment. #990 must be pretty simple if this is a parser bug, which it probably is.