refs endpoint

[dirkmc]

• make refs endpoint compatible with js-ipfs
• add refs pull stream
• move refs test to interface-js-ipfs-core (see add tests for refs endpoint interface-js-ipfs-core#460)

[lidel]

Drive-by comment: refsReadableStream is missing (ls and others have ReadableStream versions)
Missed it or was it left out on purpose?

[dirkmc]

@lidel I didn't see it used anywhere so I didn't add it. Do you know if it will be needed?

FYI I am refactoring this PR heavily to

• move most of the tests into interface-ipfs-core, so they can be used to test against go and js
• traverse the refs DAG in js-ipfs instead of relying on js-ipfs-unix-exporter, which is specifically aimed at unix format files (turns out this code is quite simple to implement with pull-traverse)

[dirkmc]

I added refsReadableStream in case it will be needed

[lidel]

Thanks! FYSA we always provide both pull-stream and readable-stream versions (see interface-js-ipfs-core/SPEC/FILES), and if streaming is supported users expect to find both.

[alanshaw]

Please update the README to include links to the docs in interface-ipfs-core.

[alanshaw]

@dirkmc I think this just needs a rebase to get the tests passing - go-ipfs 0.4.20 is broken for adding files so we've reverted to testing against 0.4.19.

[dirkmc]

@alanshaw thanks, rebased