Add JSON input (#3)

Co-authored-by: Smaug123 <patrick+github@patrickstevens.co.uk>
Reviewed-on: #3

AnkiStatic.Lib/Base91.fs

@@ -0,0 +1,24 @@
+namespace AnkiStatic
+
+open System.Text
+
+[<RequireQualifiedAccess>]
+module internal Base91 =
+
+    // Replicating the Anki algorithm
+    let private chars =
+        "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+        + "0123456789"
+        + "!#$%&()*+,-./:;<=>?@[]^_`{|}~"
+
+    let toString (input : uint64) : string =
+        let output = StringBuilder ()
+        let mutable input = input
+
+        while input > 0uL do
+            let modded = int (input % (uint64 chars.Length))
+            let div = input / (uint64 chars.Length)
+            input <- div
+            output.Append chars.[modded] |> ignore
+
+        output.ToString ()