Expose the reference UUID generator constructor

[theckman]

This change exposes the reference UUID generator in the package, so that
consumers can create a new instance and make use of it. This is being done so
that consumers can provide their own Hardware Address generation function, in
case they want to randomize the MAC address as to not expose it.

This works by now exposing the rfc4122Generator type as Gen, and adding
constructor functions that scaffold the generator appropriately. The tests were
also enhanced to confirm that the HWAddrFunc we provide is indeed being
invoked.

Fixes #41

Signed-off-by: Tim Heckman t@heckman.io

[theckman]

I'll be the first to admit that I'm not sold on this function name. Couldn't think of anything better in the moment, though.

[zerkms]

I personally tend to name things with With in such cases: NewGenWithHWAF

[theckman]

That sounds better to me.

[coveralls]

Pull Request Test Coverage Report for Build 127

• 14 of 14 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.008%) to 99.115%

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Totals
Change from base Build 123:	0.008%
Covered Lines:	336
Relevant Lines:	339

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💛 - Coveralls

[niaow]

Are we sure we even want a hwAddrFunc at all? We could alternately modify NewV1 to accept a hardware address and add a global HWAddr func to get the system hardware address instead.

So existing calls could be replaced with:

NewV1(HWAddr())

and if the user wants an alternate address:

NewV1(addr)

[zerkms]

@jadr2ddude having it as a factory function abstracts UUID client from its constructor: you as a client may generate new UUIDs and be isolated from making a decision on how and where from the hardware address is obtained from.

[theckman]

@jadr2ddude I am assuming less than 10% of users will make use of this functionality, and so I don't think it makes sense to require the 90% to consider their hardware address as part of the API they interact with. For the majority we should silently do what they expect. We can then expose knobs that allow the minority to have the control they want.