Wip1

This is the first part of network librarification. The API is the same, but code is moved to a new directory, libcfnet. The ultimate goal is to make libcfnet a separate, thread-safe library, independent of any libpromises code. We are not there yet, but dependency on the huge cf3.defs.h is removed from most of libcfnet. This will be completed when the API is overhauled. 

Some custom thread-unsafe code was removed, more will follow. Standard POSIX functions are used whenever possible, with replacements introduced in libcompat which should be used on platforms legacy platforms. Tested on Linux OK, compiles on MinGW OK.