update check against github/travis, multiple update channels (dev, prerelease, release)

[MiniDigger]

also look into the gradle versions plugin

[itsaphel]

Git hashing for versions has been set up.

Worth adding an update checker, not sure build ID is worth it.

Update checkers always tend to really annoy me, so we should figure out a way to make it less annoying.

[MiniDigger]

We can just have multiple channels, major, minor, patch, commit and then ppl can select how often they want to receive updates. We can also just auto download if ppl enable that for least possible interruptions.

[itsaphel]

Some CI API URLs:

https://ci.indices.io/job/VoxelGamesLibv2/api/json?pretty=true https://ci.indices.io/job/VoxelGamesLibv2/241/api/json?pretty=true (job #241)

The first URL unfortunately doesn't give versions. We can get versioning from the file name, but only per job. I don't know if we can attach extra params to builds and add them into the first URL.

[itsaphel]

We could maintain a map of the latest builds and serve that via a JSON API.

Jenkins, after each build, runs a shell script that checks its version and calls another API to bump the latest version for its type (e.g. if its a minor increase, update the minor increment, if its a major, update the major and minor).

Means making a little PHP script, though.