Handle Multi-site

[starfishmod]

Currently I don't think it handles multi-site well and needs to be fixed. see #3 for a reference to this

[starfishmod]

@Lewiscowles1986 you mentioned that #9 could fix this issue - can you confirm? I don't have a multi-site to test with

[Lewiscowles1986]

It works for a multi-site I tested it on which is sub-dir based; I merely followed on from other multisite plugins and the REST API, but it definitely needs more tests to catch where it falls down. Sadly I'm swamped ATM 😬