fix: fix constructor

[hugomrdias]

Level constructor call db.open which is async so we need to wait for it and
not run this in the constructor.

DO NOT MERGE #53 needs to go first

[rvagg]

Seems fine to me, but why was this necessary, was something breaking? since level defers all other operations until it's actually open, not waiting for it should still work, although it does mess up benchmarking and other measurement if you need it to be open at a specific point.

[achingbrain]

Dont know why interface-core doesn't call it...

Good question. The tests in interface-core call store.close() in the cleanup, so it should really be responsible for opening the store too.

why was this necessary, was something breaking?

Not explicitly but if you don't pass a callback to the function level exports and an error occurs while opening, it'll emit an error event which we're not listening for, so there was the possibility of the unhandled error event taking the process down.

This also updates to level 6.0.1

This pulls in level-js@5 which previously changed the default prefixing for browser datastores which out of the box meant existing repos became inaccessible.

I think this PR should only address the async-in-the-construtor problem and we should do the level update separately because it will need more testing.

[hugomrdias]

you are fast
me: git rebase --abort