Make init flags optional
The flags argument is now no longer mandatory when initialising ld-redux. If you don't specify this argument, ld-redux will subscribe to all flags in your launch darkly environment.
If you specify the argument (this is the previous behaviour), then ld-redux will only subscribe to those flags specified.
This is a non-breaking change, no action required to upgrade to this version from v3.1.2.
Refer to GH-21 for the initial motivation for this change.