Added Fsharp.FGL.IO

[LibraChris]

• read GDF Files and convert them into usable Vertex list and Edge list

[HLWeil]

Hey, could you give a little more info about the format in this PR? Also two more things are needed:

• [ ] A GDF Writer
• [ ] Documentation describing the usage of this parser (Example,ExampleOutput)

[LibraChris]

Updated Reader code to better fit the gdf format. Added Documentation for the Reader.

[LibraChris]

Known issues

• [x] Add a test for the writer

• [x] Update to dotnet 5.0.100. At the moment, only dotnet 3.1. seems to build

[LibraChris]

• [x] Review exit condition in GDF.fs -> splitElementInfos -> Handle commas

  let private splitElementInfos (line:string) =
      let chars = line.ToCharArray()
      let rec stringDeconstruction insideQuote potEmpty i vertexInfos (sb:StringBuilder) =
          match chars.[i] with
          // Handle quote marks
          | '\'' when i = chars.Length-1  -> sb.ToString() :: vertexInfos
          | '\'' when insideQuote         -> stringDeconstruction false false (i+1) vertexInfos (sb)
          | '\''                          -> stringDeconstruction true false (i+1) vertexInfos (sb)
          // Handle commas
          | ',' when insideQuote          -> stringDeconstruction insideQuote false (i+1) vertexInfos (sb.Append ',')
          | ',' when i = chars.Length-1   -> "" :: vertexInfos
          | ',' when potEmpty = true      -> stringDeconstruction false false (i+1) (""::vertexInfos) (sb.Clear())
          | ','                           -> stringDeconstruction insideQuote true (i+1) (sb.ToString() :: vertexInfos) (sb.Clear())
          // Handle every other symbol
          | c when i = chars.Length-1     -> sb.Append(c).ToString() :: vertexInfos
          | c                             -> stringDeconstruction insideQuote false (i+1) vertexInfos (sb.Append c)
  
      stringDeconstruction false false 0 [] (StringBuilder())
      |> List.rev
      |> List.toArray

[HLWeil]

If all needed for reading and writing GDF files is implemented, I'd merge this PR. What do you think, @LibraChris?

[LibraChris]

Everything should be woking fine. Thank you.

[HLWeil]

Nice Work!