feat: Add enhanced EXI viewer with XML decode capability

- Implement complete CurrentDemandReq/CurrentDemandRes parsing (24 total fields)
- Add enhanced_exi_viewer.c with detailed message analysis
- Support -decode option for clean XML output (file-ready format)
- Enable ISO1, ISO2, DIN codec support in build configuration
- Fix C99 compatibility issues in makefiles (change -ansi to -std=c99)
- Create test utilities for hex string to EXI conversion
- Generate test files: test3.exi (CurrentDemandRes), test4.exi (CurrentDemandReq)

Features:
* Dual output modes: detailed analysis (default) vs XML (-decode)
* Complete V2G message type detection and parsing
* Session ID display in hex and ASCII formats
* Voltage/current/power readings with proper units
* All optional fields and status flags supported

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

create_test_exi.c

@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* EXI codec headers */
+#include "iso1EXIDatatypes.h"
+#include "iso1EXIDatatypesEncoder.h"
+#include "ByteStream.h"
+
+#define BUFFER_SIZE 1024
+
+int main() {
+    struct iso1EXIDocument exiDoc;
+    bitstream_t stream;
+    uint8_t buffer[BUFFER_SIZE];
+    size_t pos = 0;
+    int errn = 0;
+    
+    /* Initialize EXI document */
+    init_iso1EXIDocument(&exiDoc);
+    
+    /* Create a simple V2G message */
+    exiDoc.V2G_Message_isUsed = 1;
+    init_iso1MessageHeaderType(&exiDoc.V2G_Message.Header);
+    
+    /* Set session ID to all zeros */
+    memset(exiDoc.V2G_Message.Header.SessionID.bytes, 0, 8);
+    exiDoc.V2G_Message.Header.SessionID.bytesLen = 8;
+    
+    /* Create session setup request */
+    exiDoc.V2G_Message.Body.SessionSetupReq_isUsed = 1;
+    init_iso1SessionSetupReqType(&exiDoc.V2G_Message.Body.SessionSetupReq);
+    
+    /* Set EVCC ID */
+    strcpy((char*)exiDoc.V2G_Message.Body.SessionSetupReq.EVCCID.bytes, "01");
+    exiDoc.V2G_Message.Body.SessionSetupReq.EVCCID.bytesLen = 2;
+    
+    /* Setup output stream */
+    stream.size = BUFFER_SIZE;
+    stream.data = buffer;
+    stream.pos = &pos;
+    stream.buffer = 0;
+    stream.capacity = 8;
+    
+    /* Encode to EXI */
+    printf("Encoding V2G message to EXI...\n");
+    errn = encode_iso1ExiDocument(&stream, &exiDoc);
+    
+    if (errn != 0) {
+        printf("Encoding failed with error: %d\n", errn);
+        return -1;
+    }
+    
+    /* Write to file */
+    FILE *fp = fopen("test_message.exi", "wb");
+    if (fp == NULL) {
+        printf("Cannot create output file\n");
+        return -1;
+    }
+    
+    fwrite(buffer, 1, pos, fp);
+    fclose(fp);
+    
+    printf("Created test_message.exi with %zu bytes\n", pos);
+    return 0;
+}