Initial plan for auto-updates and versioning

[nylen]

Here is the basic idea:

• Nightly versions can update to newer nightly ~, alpha, beta, or final release~ builds (if you're on nightly builds you're a developer, and you probably want to keep getting new nightly builds only)
• Alpha versions can update to newer alpha, beta, or final release builds
• Beta versions can update to newer beta or final release builds
• Final release versions can update to newer final release builds (without moving to a new semver major version i.e. 1.2.3 => 2.0.0)

Open question: this means that all auto-updates will eventually funnel towards final release builds and stay there. Is this desirable? We may need an option for whether to stay on the same "release channel" (nightly, alpha, beta, final) or not (or the ability to "switch channels").

From @invisnet here are some possible auto-update before => after versions (lines without => mean "no change"):

Step 1
======
1.0.0-alpha1+build.20181021 => 1.0.0-alpha1+build.20181021
1.0.0-alpha1+build.20181020 => 1.0.0-alpha1+build.20181021
1.0.0-alpha1 => 1.0.0-alpha1

Step 2
======
1.0.0-alpha1+build.20181021 => 1.0.0-alpha1+build.20181021
1.0.0-alpha1+build.20181020 => 1.0.0-alpha1+build.20181021
1.0.0-alpha2 => 1.0.0-alpha2
1.0.0-alpha1 => 1.0.0-alpha2

Step 3
======
1.0.0-alpha1+build.20181021 => 1.0.0-alpha1+build.20181021
1.0.0-alpha1+build.20181020 => 1.0.0-alpha1+build.20181021
1.0.0-alpha2 => 1.0.0-beta1
1.0.0-beta1 => 1.0.0-beta1
1.0.0-alpha1 => 1.0.0-beta1

Step 4
======
1.0.0-beta1 => 1.0.0-beta1
1.0.0-alpha2 => 1.0.0-beta1
1.0.0-alpha1 => 1.0.0-beta1
1.0.0-beta2+build.20181028 => 1.0.0-beta2+build.20181028
1.0.0-alpha1+build.20181021 => 1.0.0-beta2+build.20181028
1.0.0-alpha1+build.20181020 => 1.0.0-beta2+build.20181028

Step 5
======
1.0.0-beta2 => 1.0.0-beta2
1.0.0-beta1 => 1.0.0-beta2
1.0.0-alpha2 => 1.0.0-beta2
1.0.0-alpha1 => 1.0.0-beta2
1.0.0-beta2+build.20181030 => 1.0.0-beta2+build.20181030
1.0.0-beta2+build.20181028 => 1.0.0-beta2+build.20181030
1.0.0-alpha1+build.20181021 => 1.0.0-beta2+build.20181030
1.0.0-alpha1+build.20181020 => 1.0.0-beta2+build.20181030

Step 6
======
1.0.0-beta2 => 1.0.0
1.0.0-beta1 => 1.0.0
1.0.0 => 1.0.0
1.0.0-alpha2 => 1.0.0
1.0.0-alpha1 => 1.0.0
1.0.0-beta2+build.20181030 => 1.0.0+build.20181031
1.0.0-beta2+build.20181028 => 1.0.0+build.20181031
1.0.0-alpha1+build.20181021 => 1.0.0+build.20181031
1.0.0-alpha1+build.20181020 => 1.0.0+build.20181031
1.0.0+build.20181031 => 1.0.0+build.20181031

Step 7
======
1.0.0-beta2 => 1.1.0-alpha1
1.0.0-beta1 => 1.1.0-alpha1
1.0.0 => 1.0.0
1.1.0-alpha1 => 1.1.0-alpha1
1.0.0-alpha2 => 1.1.0-alpha1
1.0.0-alpha1 => 1.1.0-alpha1
1.0.0-beta2+build.20181030 => 1.1.0-alpha1+build.20181101
1.1.0-alpha1+build.20181101 => 1.1.0-alpha1+build.20181101
1.0.0-beta2+build.20181028 => 1.1.0-alpha1+build.20181101
1.0.0-alpha1+build.20181021 => 1.1.0-alpha1+build.20181101
1.0.0-alpha1+build.20181020 => 1.1.0-alpha1+build.20181101
1.0.0+build.20181031 => 1.1.0-alpha1+build.20181101

[invisnet]

That was a first PoC; now updated:

Step 1
======
1.0.0-alpha1+build.20181021
1.0.0-alpha1

Step 2
======
1.0.0-alpha1+build.20181021
1.0.0-alpha2
1.0.0-alpha1 => 1.0.0-alpha2

Step 3
======
1.0.0-alpha1+build.20181021
1.0.0-beta1
1.0.0-alpha2 => 1.0.0-beta1
1.0.0-alpha1 => 1.0.0-beta1

Step 4
======
1.0.0-beta1
1.0.0-beta2+build.20181028
1.0.0-alpha2 => 1.0.0-beta1
1.0.0-alpha1 => 1.0.0-beta1
1.0.0-alpha1+build.20181021 => 1.0.0-beta2+build.20181028
1.0.0-alpha1+build.20181020 => 1.0.0-beta2+build.20181028

Step 5
======
1.0.0-beta2+build.20181030
1.0.0-beta2
1.0.0-beta1 => 1.0.0-beta2
1.0.0-alpha2 => 1.0.0-beta2
1.0.0-alpha1 => 1.0.0-beta2
1.0.0-alpha1+build.20181021 => 1.0.0-beta2+build.20181030
1.0.0-alpha1+build.20181020 => 1.0.0-beta2+build.20181030

Step 6
======
1.0.0+build.20181031
1.0.0
1.0.0-beta2 => 1.0.0
1.0.0-beta1 => 1.0.0
1.0.0-alpha2 => 1.0.0
1.0.0-alpha1 => 1.0.0
1.0.0-beta2+build.20181030 => 1.0.0+build.20181031
1.0.0-beta2+build.20181028 => 1.0.0+build.20181031
1.0.0-alpha1+build.20181021 => 1.0.0+build.20181031
1.0.0-alpha1+build.20181020 => 1.0.0+build.20181031

Step 7
======
1.0.0
1.1.0-alpha1+build.20181101
1.1.0-alpha1
1.0.0-beta2 => 1.0.0
1.0.0-beta1 => 1.0.0
1.0.0-alpha2 => 1.0.0
1.0.0-alpha1 => 1.0.0
1.0.0-beta2+build.20181030 => 1.1.0-alpha1+build.20181101
1.0.0-beta2+build.20181028 => 1.1.0-alpha1+build.20181101
1.0.0-alpha1+build.20181021 => 1.1.0-alpha1+build.20181101
1.0.0-alpha1+build.20181020 => 1.1.0-alpha1+build.20181101
1.0.0+build.20181031 => 1.1.0-alpha1+build.20181101

Each step is a point in time, and each line without a => is an actual lump of json.

The major change in logic is that a prerelease should update to the next full release, not the latest prerelease.

[nylen]

This is implemented in the latest commits, and now live at https://api-v1.classicpress.net/upgrade/. Closing; we can track specific follow-up tasks in new issues.