Update to NetCore 3.1, added Kestrel for REST api and few basic endpoints.

ASS.Server/Web/Controllers/ByondController.cs

@@ -0,0 +1,31 @@
+using ASS.Server.Services;
+using Microsoft.AspNetCore.Mvc;
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace ASS.Server.Web.Controllers
+{
+
+    [ApiController]
+    [Route("[controller]")]
+    public class ByondController : ControllerBase
+    {
+
+        ByondService byondService;
+
+        public ByondController(ByondService bs)
+        {
+            byondService = bs;
+        }
+
+        [HttpPost("install/{major}.{minor}")]
+        public async Task<int> InstallVersionAsync(int major, int minor)
+        {
+            await byondService.SwitchToVersion(new API.ByondVersion() { Major = major, Minor = minor });
+            return 0;
+        }
+
+    }
+}