Add Array.pluck function

[jeparlefrancais]

Closes #16

Add Array.pluck to map an array to one of its field.

local rows = {
    { id = 1, name = 'Ada' },
    { id = 2, name = 'Grace' },
}
local names = Array.pluck(rows, 'name')
-- names is { 'Ada', 'Grace' }

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• add entry to the changelog
• update relevant documentation