[WIP] refactor: use CIDv1 and encode with base32 by default

[alanshaw]

BREAKING CHANGE: CIDs created by this module will default to v1 and will be base32 encoded by default.

refs ipfs/js-ipfs#1440

@achingbrain I could use your advice on the wisdom of this particular change. I think it's fine, I just wanted to confirm. It's used by these tests:

    ✓ results in the same hash as a sharded directory created by the importer when adding a new file (49ms)
    ✓ results in the same hash as a sharded directory created by the importer when creating a new subshard (75ms)
    ✓ results in the same hash as a sharded directory created by the importer when adding a file to a subshard (50ms)
    ✓ results in the same hash as a sharded directory created by the importer when adding a file to a subshard of a subshard (851ms)

I've added rawLeaves: false because switching to CIDv1 enables it by default in unixfs-importer but MFS explicitly disables it, hence we have to explicitly set it to false when calling unixfs-importer in order to get the same hash.

Depends on:

• [WIP] refactor: use CID v1 with base32 encoding by default js-ipfs-unixfs-importer#21
• refactor: base32 encode CIDs by default multiformats/js-cid#73