Achievement milestones at non-round numbers

[smichel17]

I would expect to get achievements at round numbers, but I frequently get them at seemingly-arbitrary numbers. Ex:

I don't really mind it — it makes the achievements seem more like things that randomly pop up every so often than goals I'm working towards, which may even be good — but it does seem odd, so I wonder if it's a bug.

[matkoniecz]

I was also surprised, but right now achievements are simply defined in such way.

I admit that I considered making PR changing that but was not bothered sufficiently to implement anything.

            R.string.achievement_surveyor_solved_X,
            TotalSolvedQuests,
            // levels: 10, 30, 60, 100, 150, 210, 280, 360, 450, 550, 660, 780, 910, 1050, ...
            { lvl -> (lvl + 1)*10 },

Or in this specific case:

StreetComplete/app/src/main/java/de/westnordost/streetcomplete/data/user/achievements/AchievementsModule.kt

Line 385 in 6065361

// levels: 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, ...

- you get new level every 4 days of mapping