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>

Debug/makefile

@@ -0,0 +1,51 @@
+################################################################################
+# Automatically-generated file. Do not edit!
+################################################################################
+
+-include ../makefile.init
+
+RM := rm -rf
+
+# All of the sources participating in the build are defined here
+-include sources.mk
+-include src/xmldsig/subdir.mk
+-include src/transport/subdir.mk
+-include src/test/subdir.mk
+-include src/iso2/subdir.mk
+-include src/iso1/subdir.mk
+-include src/din/subdir.mk
+-include src/codec/subdir.mk
+-include src/appHandshake/subdir.mk
+-include subdir.mk
+-include objects.mk
+
+ifneq ($(MAKECMDGOALS),clean)
+ifneq ($(strip $(C_DEPS)),)
+-include $(C_DEPS)
+endif
+endif
+
+-include ../makefile.defs
+
+# Add inputs and outputs from these tool invocations to the build variables 
+
+# All Target
+all: OpenV2G.exe
+
+# Tool invocations
+OpenV2G.exe: $(OBJS) $(USER_OBJS)
+	@echo 'Building target: $@'
+	@echo 'Invoking: MinGW C Linker'
+	gcc  -o "OpenV2G.exe" $(OBJS) $(USER_OBJS) $(LIBS)
+	@echo 'Finished building target: $@'
+	@echo ' '
+
+# Other Targets
+clean:
+	-$(RM) $(EXECUTABLES)$(OBJS)$(C_DEPS) OpenV2G.exe
+	-@echo ' '
+
+.PHONY: all clean dependents
+.SECONDARY:
+
+-include ../makefile.targets