Implement public API

[atomflunder]

When I am doing a rewrite of this project, I want to include a free, publicly accessible API.
The frontend will probably just call that instead of doing the calculations itself.

Possible request body:

{
  "config": {
    "beta": 4.166,
    "tau": 0.0833,
    "drawProbability": 0.1
  },
  "teams": [
    {
      "name": "Team Alpha",
      "players": [
        {
          "name": "Alice",
          "rating": [25, 8.333],
          "weight": 1
        },
        {
          "name": "Bob",
          "rating": [27, 7.5],
          "weight": 1
        }
      ],
      "rank": 1
    },
    {
      "name": "Team Beta",
      "players": [
        {
          "name": "Charlie",
          "rating": [23, 9.0],
          "weight": 1
        },
        {
          "name": "Dana",
          "rating": [26, 8.0],
          "weight": 1
        }
      ],
      "rank": 2
    }
  ]
}

Possible response body:

{
  "teams": [
    {
      "name": "Team Alpha",
      "rank": 1,
      "expectedScore": 0.67,
      "players": [
        {
          "name": "Alice",
          "rating": [25, 8.333],
          "weight": 1,
          "ratingChanges": [1.2, -0.4]
        },
        {
          "name": "Bob",
          "rating": [27, 7.5],
          "weight": 1,
          "ratingChanges": [0.9, -0.3]
        }
      ]
    },
    {
      "name": "Team Beta",
      "rank": 2,
      "expectedScore": 0.33,
      "players": [
        {
          "name": "Charlie",
          "rating": [23, 9.0],
          "weight": 1,
          "ratingChanges": [-1.1, 0.5]
        },
        {
          "name": "Dana",
          "rating": [26, 8.0],
          "weight": 1,
          "ratingChanges": [-0.8, 0.4]
        }
      ]
    }
  ],
  "matchQuality": 0.91
}