## Security Fixes
- Fix memory leak: piStartRef was not freed in cleanup paths
- Add NULL checks after all malloc/calloc calls to prevent crashes
- Add compiler security flags: -fstack-protector-strong, -D_FORTIFY_SOURCE=2, -Wformat-security

## Code Modernization
- Modernize CMakeLists.txt with proper Release/Debug build separation
- Use target-based CMake properties instead of global definitions
- Add -Wpedantic flag (with exception for 3rdparty getopt code)
- Update copyright years to 2015-2025
- Update libmodbus minimum version to 3.1.7
- Translate all French comments to English

## Community PR Integration
- Implement PR epsilonrt#87: Check modbus_set_slave() return value to prevent crashes with invalid slave addresses (credit: @r00t-)
- Implement PR epsilonrt#90: Add -x option to print register addresses in hexadecimal format (credit: @ciakval)
- Implement PR epsilonrt#99: Add -Q and -X options for libmodbus quirks (MAX_SLAVE and REPLY_TO_BROADCAST) (credit: @JesseRiemens)

## New Features
- `-x` Print address (reference) in hexadecimal format
- `-Q` Enable MAX_SLAVE quirk (accept slave id 0-255)
- `-X` Enable REPLY_TO_BROADCAST quirk (send reply to broadcast)

## CI/CD
- Add GitHub Actions workflow for automated builds on Linux, macOS, and Windows

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

…ibution

Remove the implementations of:
- modbus_set_slave() return value checking (originally PR epsilonrt#87 by @r00t-)
- -x hex address option (originally PR epsilonrt#90 by @ciakval)
- -Q/-X quirks options (originally PR epsilonrt#99 by @JesseRiemens)

These features will be re-added in subsequent commits with proper git
authorship attributed to their original contributors.

Add -x command-line option to print register/coil addresses in
hexadecimal format (0x%04X) instead of decimal. Useful for debugging
devices with hex-addressed register maps.

Originally contributed in PR epsilonrt#90; adapted to the current codebase.

Signed-off-by: Jan Remes <jan.remes@mycroftmind.com>

Add -x command-line option to print register/coil addresses in
hexadecimal format (0x%04X) instead of decimal. Useful for debugging
devices with hex-addressed register maps.

Originally contributed in PR epsilonrt#90; adapted to the current codebase.

Signed-off-by: Jan Remes <jan.remes@mycroftmind.com>