Add go.mod and go.sum files to support Go modules.

[creachadair]

This commit contains no functional changes; it's just adding config files for the Go modules facility. Ideally this commit should also be accompanied by a new version tag, since the current latest tag is v1.0.0 from Nov. 2017, and several optimizations have been added since then.

[creachadair]

Clearly the CI is in some way discontent with this change, I'm trying to work out why.

[creachadair]

Ah, I think I see the problem. The last successful CI build was 6 months ago on #94, and since then the errcheck golint package has updated to depend on Go ≥ 1.9. The Travis config for 1.8 will therefore no longer work at all, irrespective of modules.

Edit: Correct which package was afflicted.

[creachadair]

Indeed, CI fails at HEAD: https://travis-ci.org/sergi/go-diff/jobs/488608466. So this PR didn't cause any new problems, but there are some existing ones that will need fixed. I'll look into that separately.

[creachadair]

Ok, I was able to fix the import path issue for golang.org/x/lint for 1.9, but 1.8 remains broken because the API is no longer compatible. Specifically, 1.8 predates type alias support.

[creachadair]

I suggest dropping support for Go 1.8 entirely. Even though this repo only depends on golint as a verification tool, the dependency compatibility problem runs deeper. To address it you'll need to either install a newer version of Go to build golint, or find an older binary release to depend on (which golint does not itself provide).

[creachadair]

After that somewhat noisy debugging, I think this is ready for a review.

[creachadair]

I'm not sure who maintains the package, but if someone would be willing to take a look and let me know if this seems reasonable, I'd be grateful! I'm happy to address any concerns promptly.

[creachadair]

Ping! Is someone available to take a look and let me know whether you consider this a reasonable change? Thanks.

[creachadair]

Ping! @sergi do you have any thoughts about this proposed change?

[creachadair]

Ping! Is anyone maintaining this package, and willing to offer comment about this change?

[creachadair]

Ping! Can someone please take a look at this change? Even if you have concerns or objections, it would be helpful for us to know what they are. Thanks.

[creachadair]

Ping! Is someone available to take a look and let me know whether you consider this a reasonable change? Thanks.

[creachadair]

Ping! Can you please take a look when you have time?

[paper777]

@sergi PING PTAL Thanks!

[creachadair]

Ping, @sergi. Please have a look when you can, thanks.

[creachadair]

@sergi Please take a look when you are able.

[creachadair]

Hi, @sergi, I'd be grateful for a review when you are able. Thanks!

[creachadair]

Greetings, @sergi! Please take a look when you have some time.

[creachadair]

Dear @sergi, can you please have a look at this PR when you have time? Thanks!

[edocevol]

@sergi Please review PR~~~

[creachadair]

Hello, @sergi, when you have some available bandwidth, I'd be very grateful for a review here. If you have any questions or concerns about the change, I'll do my best to address them. Or if you disagree with the change entirely, it would be helpful to know why. Thanks!

[creachadair]

Thank you!

[creachadair]

Would you like me to squash the commits before merge?

[creachadair]

I went ahead and pre-squashed the commits so the merge will be clean once CI completes.

[creachadair]

Hi, @sergi, I think this is ready for a merge now (I don't have write access). Thanks!

[creachadair]

Hi, @sergi, I've updated the Travis CI config to include Go 1.13 now that it has been released, and added the new Go tool version tag to go.mod. Once CI clears this should be ready to merge at your convenience.