Add API to return all keys in store

[dwhogg]

Suggest having a call like keys(callback) to return an array of all keys in store. Would be useful in cases of trying to do housekeeping on the store if max size being reached.

[tofumatt]

I'm definitely cool with this; I'd like for 1.1 to support a lot of multi-key APIs; getItems and keys for sure, possibly setItems and removeItems as well.

[omggga]

Hello from 2017!

Still not possible to remove several keys with one call?

Now making this one

Promise.all([
    localforage.removeItem(key1),
    localforage.removeItem(key2)
]).then(function(res) {
    console.log(res);
});

could be more beautiful if

localforage.removeItems([key1, key2, key3]).then(function() { } );

[thgreasi]

https://github.com/localForage/localForage-removeItems :)

[omggga]

Oh, thank you!