Added keyword for multi-binding let

Program.cs

@@ -109,6 +109,7 @@ public enum TokenType
 	When,
 	Is,
 	Let,
+	And,
 	In,
 	With,
 	Fn,
@@ -137,6 +138,7 @@ class Scanner
 		{"when", TokenType.When},
 		{"is", TokenType.Is},
 		{"let", TokenType.Let},
+		{"and", TokenType.And},
 		{"in", TokenType.In},
 		{"with", TokenType.With},
 		{"fn", TokenType.Fn},