GetAll() should return an iterator for the key-value items about nutsdb

[xujiajun]

Hey @xujiajun Can I work on this issue?

You can go to this post to reply to participate nutsdb/proposal#3

[xujiajun]

hi, @Ice3man543

Pull request welcome!

Don't forget compatible with all modes, like this:

	if idxMode == HintBPTSparseIdxMode {
	  ...
	}

	if idxMode == HintKeyValAndRAMIdxMode || idxMode == HintKeyAndRAMIdxMode {
          ...
        }

Thanks.

[zeina1i]

Hey @xujiajun
Can I work on this issue?

[xujiajun]

@zeina1i Contributions welcome :)