feat: support UnixFSv1.5 metadata (#2621)

* feat: support UnixFSv1.5 metadata

Adds metadata support.

Specifying metadata:

```console
$ jsipfs add --mode=0777 --mtime=100000 ./foo.txt
```

Respecting exsting metadata:

```console
$ jsipfs add --preserve-mode --preserve-mtime ./foo.txt
```

Displaying metadata:

```console
$ jsipfs ls Qmfoo
-rw-r--r-- Nov 21, 2019, 09:46:23 AM CST bar.txt Qbar 0
```

* chore: update dep paths and jsdocs

* chore: fix linting

* fix: expose metadata in http api

* test: interface tests passing

* chore: update package.json with branches

* fix: support mtime as timespec

* fix: check mtime formatting in timezone agnostic way

* fix: do not run hrtime tests in the browser

* chore: upgrade interop tests

* chore: symlink ipfs dir for interop tests

* fix: build ipfs before running examples

* fix: expose mtime-nsecs to cli and add tests

* fix: export path to js-ipfs binary

* fix: support optional mtime

* fix: linting

* fix: pin datastore-pubsub version due to ipfs/js-datastore-pubsub#20

* chore: restore datastore-pubsub semver

Author: achingbrain

running-multiple-nodes/test.js

@@ -1,6 +1,6 @@
 'use strict'
 
-const IPFS = require('ipfs')
+const IPFS = require('../../')
 
 const execa = require('execa')
 const os = require('os')