Initial version of freemodbus master port files have been added to ESP-IDF based on https://github.com/armink/FreeModbus_Slave-Master-RTT-STM32.
The overall repository license, at the time of adding these files, has been BSD 3-clause. However at that time, several port files carried LGPL license headers. As the author of these files confirmed in https://github.com/armink/FreeModbus_Slave-Master-RTT-STM32/issues/61#issuecomment-977828450, this wasn't intentional. ESP-IDF version of modbus master port has been rewritten to target FreeRTOS instead of RT-Thread, but the license headers remained from the original version. This commit corrects this, replacing the license of these files with BSD 3-clause.
Contains two different component folders per each implementation (serial_master and serial_slave) with concrete ports.
Added common public api for master and slave and common interface for master and slave implementation.
Add support of cmake system (added cmake files).
Added sdkconfig.defaults files for slave and master modbus examples.
Updated make file and KConfig for freemodbus component
Update according to review and fix doxygen warnings
Fix Doxyfile to pass documentation build
Update headers and change interface file names as per review comments
Merge branch feature/freemodbus_move_rs485_mode_control
Update after review:
The stack modbus folder updated to support master and slave ports together and moved into freemodbus/modbus
Stack and port files updated to remove duplicated simbols
Make file, KConfig and CMakeLists.txt updated to compile master and slave stacks, common interface and concrete implementations of ports
Stack callback functions execute callbacks using interface pointer from concrete port implementation
User can instantiate any of concrete port using common API (only one concrete port at a time) and it does not require to select port by KConfig
Port pins and mode configuration moved into example files from port files to allow user select pins and port mode (customer request)
Changes tested using pymodbus, ModbusPoll and communication between two boards
Updated DoxyFile according to public include path
Fix maximum instance size for slave (merge from master of customer issue)
Fix critical section issue TW#28622 (change spin lock based critical section to semaphore)
Move serial port files into component port folder for master and slave accordingly
Fix example issue showed in the log when IO slave is not configured correctly
Fix conflicts while merging from origin/master
Fix errors handling in modbus controller interface + some final corrections according to review
Update maximum allowed number of slaves in the network segment
Fix bug with incorrect coils read mask
Closes https://github.com/espressif/esp-idf/issues/858
