Implement sqlite REGEXP

Elwig/Windows/QueryWindow.xaml.cs

@@ -3,6 +3,7 @@ using Microsoft.Data.Sqlite;
 using System;
 using System.Collections.Generic;
 using System.Data.Common;
+using System.Text.RegularExpressions;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Data;
@@ -26,6 +27,7 @@ namespace Elwig.Windows {
             IList<DbColumn> header;
 
             using (var cnx = new SqliteConnection(AppDbContext.ConnectionString)) {
+                cnx.CreateFunction<string, string?, bool?>("REGEXP", (pattern, value) => value == null ? null : Regex.Match(value, pattern).Success, true);
                 cnx.Open();
                 var cmd = cnx.CreateCommand();
                 cmd.CommandText = sqlQuery;