Revert Xor / Either changes for 0.7.0 release

[travisbrown]

We'd planned to start the switch from Xor to Either in Cats 0.8, but several of the Either pull requests just got merged, and 0.7.0 isn't out yet:

• Replace Xor with Either, fixes #1192 #1289
• Port #1215 to EitherT #1301
• https://github.com/47deg/cats/pull/1

(The last one will only need to be reverted if we're trying to get #1266 into 0.7.0, which I think would be a good idea, since it's ready now, and since it's at least part of what we've been waiting for.)

Up until now we've been tagging and publishing 0.x.0 releases from master, and I don't see any reason to make that more complicated now, so I think at least #1289 and #1301 will need to be reverted before the 0.7.0 release.

[non]

👍 to this plan

I think I gave @adelbertc the wrong idea when I signed-off on #1289. Apologies!

I propose that I:

• un-merge Replace Xor with Either, fixes #1192 #1289 and Port #1215 to EitherT #1301
• merge Draft of 0.7.0 release notes #1259 and FreeT stack-safe transformer #1266
• release 0.7.0
• re-merge Replace Xor with Either, fixes #1192 #1289 and Port #1215 to EitherT #1301
• celebrate

What do people think? We don't often revert things, I'd like to get at least 1-2 other +1s on this plan.

[travisbrown]

👍 to @non's plan, with one additional piece:

• https://github.com/47deg/cats/pull/2 to revert https://github.com/47deg/cats/pull/1 before FreeT stack-safe transformer #1266 gets merged

I've also just opened #1303 for the #1301 reversion. GitHub isn't letting me open a revert PR for #1289, and the error message is unclear, so I'm not sure whether reverting #1301 will fix the situation. (This is probably an argument for rebasing big PRs before merging.)

[kailuowang]

👍 i vote for let's wrap asap before more confusion

[adelbertc]

I'm so sorry guys! I completely forgot about the 0.7.0 release - I saw the approvals so I clicked merge and moved on. :( :( Of course 👍 from me

[non]

Here's a PR where I'm doing it: #1305

[non]

Alright, as-per discussions on Gitter it seems like we've decided to hold off doing a full-scale revert and instead just revert the existing API changes (to minimize 0.6.1 -> 0.7.0 breakage). This will make the future 0.7.x -> 0.8.0 upgrade path less painful.

@adelbertc agreed to take point on this.

[non]

This was fixed by #1306.