New exercism problem done

exercism/fsharp/darts/Darts.fs

+module Darts
+
+let withinCircle (radius: int) (x: double) (y: double) =
+    sqrt ((pown x 2) + (pown y 2)) <= double(radius)
+
+let score (x: double) (y: double): int =
+    if withinCircle 10 x y then
+        if withinCircle 5 x y then
+            if withinCircle 1 x y then
+                10
+            else
+                5
+        else
+            1
+    else 0

exercism/fsharp/darts/Darts.fsproj

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Darts.fs" />
+    <Compile Include="DartsTests.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.6.1" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.2" />
+    <PackageReference Include="FsUnit.xUnit" Version="3.8.1" />
+  </ItemGroup>
+
+</Project>

exercism/fsharp/darts/DartsTests.fs

+// This file was auto-generated based on version 2.2.0 of the canonical data.
+
+module DartsTests
+
+open FsUnit.Xunit
+open Xunit
+
+open Darts
+
+[<Fact>]
+let ``Missed target`` () =
+    score -9.0 9.0 |> should equal 0
+
+[<Fact>]
+let ``On the outer circle`` () =
+    score 0.0 10.0 |> should equal 1
+
+[<Fact>]
+let ``On the middle circle`` () =
+    score -5.0 0.0 |> should equal 5
+
+[<Fact>]
+let ``On the inner circle`` () =
+    score 0.0 -1.0 |> should equal 10
+
+[<Fact>]
+let ``Exactly on centre`` () =
+    score 0.0 0.0 |> should equal 10
+
+[<Fact>]
+let ``Near the centre`` () =
+    score -0.1 -0.1 |> should equal 10
+
+[<Fact>]
+let ``Just within the inner circle`` () =
+    score 0.7 0.7 |> should equal 10
+
+[<Fact>]
+let ``Just outside the inner circle`` () =
+    score 0.8 -0.8 |> should equal 5
+
+[<Fact>]
+let ``Just within the middle circle`` () =
+    score -3.5 3.5 |> should equal 5
+
+[<Fact>]
+let ``Just outside the middle circle`` () =
+    score -3.6 -3.6 |> should equal 1
+
+[<Fact>]
+let ``Just within the outer circle`` () =
+    score -7.0 7.0 |> should equal 1
+
+[<Fact>]
+let ``Just outside the outer circle`` () =
+    score 7.1 -7.1 |> should equal 0
+
+[<Fact>]
+let ``Asymmetric position between the inner and middle circles`` () =
+    score 0.5 -4.0 |> should equal 5
+

exercism/fsharp/darts/README.md

+# Darts
+
+Write a function that returns the earned points in a single toss of a Darts game.
+
+[Darts](https://en.wikipedia.org/wiki/Darts) is a game where players
+throw darts to a [target](https://en.wikipedia.org/wiki/Darts#/media/File:Darts_in_a_dartboard.jpg).
+
+In our particular instance of the game, the target rewards with 4 different amounts of points, depending on where the dart lands:
+
+* If the dart lands outside the target, player earns no points (0 points).
+* If the dart lands in the outer circle of the target, player earns 1 point.
+* If the dart lands in the middle circle of the target, player earns 5 points.
+* If the dart lands in the inner circle of the target, player earns 10 points.
+
+The outer circle has a radius of 10 units (This is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered to the same point (That is, the circles are [concentric](http://mathworld.wolfram.com/ConcentricCircles.html)) defined by the coordinates (0, 0).
+
+Write a function that given a point in the target (defined by its `real` cartesian coordinates `x` and `y`), returns the correct amount earned by a dart landing in that point.
+## Running the tests
+
+To run the tests, run the command `dotnet test` from within the exercise directory.
+
+## Autoformatting the code
+
+F# source code can be formatted with the [Fantomas](https://github.com/fsprojects/fantomas) tool.
+
+After installing it with `dotnet tool restore`, run `dotnet fantomas .` to format code within the current directory.
+
+## Further information
+
+For more detailed information about the F# track, including how to get help if
+you're having trouble, please visit the exercism.io [F# language page](http://exercism.io/languages/fsharp/resources).
+
+## Source
+
+Inspired by an exercise created by a professor Della Paolera in Argentina
+