finish rewrite; port to cmake, loads of other changes

Theres documentation at https://sylvessa.zip/fourkit/ now. And a bunch of other changes. Check the discord server for a more comprehensive list

Minecraft.Server.FourKit/Event/EventHandlerAttribute.cs

@@ -0,0 +1,40 @@
+namespace Minecraft.Server.FourKit.Event;
+
+/// <summary>
+/// Marks a method inside a <see cref="Listener"/> as an event handler.
+/// This class is not named "EventHandler" due to a naming conflict with the existing System.EventHandler
+/// </summary>
+[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
+public sealed class EventHandlerAttribute : Attribute
+{
+    /// <summary>
+    /// Priority of this handler. Lower values run first.
+    /// Default is <see cref="EventPriority.Normal"/>.
+    /// </summary>
+    public EventPriority Priority { get; set; } = EventPriority.Normal;
+
+    /// <summary>
+    /// Whether this handler should be skipped when the event is already
+    /// cancelled by a lower-priority handler. Default is <c>false</c>.
+    /// </summary>
+    public bool IgnoreCancelled { get; set; } = false;
+}
+
+/// <summary>
+/// Execution priority for event handlers.
+/// </summary>
+public enum EventPriority
+{
+    /// <summary>Event call is of very low importance and should be ran first, to allow other plugins to further customise the outcome</summary>
+    Lowest = 0,
+    /// <summary>Event call is of low importance</summary>
+    Low = 1,
+    /// <summary>Event call is neither important nor unimportant, and may be ran normally</summary>
+    Normal = 2,
+    /// <summary>Event call is of high importance</summary>
+    High = 3,
+    /// <summary>Event call is critical and must have the final say in what happens to the event</summary>
+    Highest = 4,
+    /// <summary>Event is listened to purely for monitoring the outcome of an event. Should not modify the event.</summary>
+    Monitor = 5
+}