#13 POSIX compliance

With the goal of targeting minimal platforms, rewriting in ANSI C would be desirable:

• Set -std=c11 in compile flags
• Rewrite or eliminate GNU extensions: strdup, fmemopen, etc.
• Verify dependencies, both embedded and dynamically linked (LMDB may not be ANSI C, so the target systems would have to be able to support installing it separately)

This may be never attainable, as LMDB relies on POSIX. Unless a switch to compile without LMDB support, using a valid alternative, is added, targeting POSIX may be more realistic and still a valuable improvement.