What is the intention of the ports/posix #1059

The OS based apps/ examples (aka bacnet-tools) rely on some OS features such as files that embedded microcontrollers don't usually have in a standard way. I'm working on some proof-of-concept BACnet File object work on microcontrollers, and I wanted to reduce maintenance of the BACnet File object and AtomicReadFile and AtomicWriteFile code. Over the years I've copied and ported bacfile.c for numerous file stores such as CFS (coffee from Contiki), littleFS, POSIX, flash blocks, EEPROM, and static content. I refactored the bacfile.c file stream & record read & write and size operations into callbacks, and that meant that the interface to the OS based apps/ needing file services which can be POSIX and applied across the major OS in ports (win32, bsd, linux).

I had also moved src/datalink/dlenv.c into ports/posix but reverted that at the last minute as that was too drastic for the moment. I would like to move dlenv.c somewhere out of the src/datalink tree - perhaps the next major revision. If there is a better place to put modules that only apply to OS based apps/ for your workflow, please share. Maybe in an apps/posix folder instead of ports, similar to where apps/lib is sitting?

At some point in the future, I would also like to add a CMakeLists.txt to apps/lib and refactor the root CMakeLists.txt - it was part of a contributed change at one point, but I'm not a CMake expert and don't know what a best practice would be.