pattern: Atari 8-bit binary format (XEX) (#453)

* add atari XEX format

* Update README.md

---------

Co-authored-by: Nik <werwolv98@gmail.com>

patterns/xex.hexpat

@@ -0,0 +1,34 @@
+#pragma author Adiee5
+#pragma description Atari 8-bit binary format (.xex)
+#pragma endian little
+#pragma magic [ FF FF ] @ 0
+
+import std.mem;
+import std.io;
+
+u16 header @ 0;
+
+if (header != 0xFFFF)
+    std::error("Not a valid XEX file");
+    
+fn hex_dec_addr(u16 num){
+    return std::format("0x{:04X} ({})", num, num);
+};
+
+struct block {
+    u16 start [[comment("Address of the first byte"), format("hex_dec_addr")]];
+    if (start == 0xFFFF) continue; //an unnecessary header to be ignored
+    u16 end [[comment("Address of the last byte"), format("hex_dec_addr")]];
+    
+    // since 1 and 2 byte blocks sometimes have special meanings,
+    // we make them regural variables instead of byte arrays, 
+    // so that reading their values from the GUI is easier
+    match (end-start){
+        (0): u8 data;
+        (1): u16 data [[format("hex_dec_addr")]];
+        (_): u8 data[end-start+1];
+    }
+        
+};
+
+block data_blocks[while(!std::mem::eof())] @ 2 [[name("Data Blocks")]];