Portability to Windows

[attipaci]

Currently RedisX builds on POSIX (Linux, MacOS, BSD, Cygwin, WSL), but not natively on Windows. A number of changes will be necessary to enable Windows builds:

• portable mutexes (via xmutex.h from the upcoming xchange 1.2.0 dependency)
• Thread managements (create, detach, join) for windows without the POSIX pthread library (may eliminate Threads dependence on WIN32).
• Use <io.h> instead of unistd.h, and _close() / _access() instead of UNIX close() / access().
• Use _getch() from <conio.h> for parsing passwords in redisx-cli on Windows. (Eliminates libbsd dependence on WIN32).
• Enable windows-latest in build-cmake.yml matrix.
• Update README