Bugfix release

• register_virtual_function cannot exhaust the buffers any more
• do not write over the boundary of the buffer that contains the stack trace
• print better warnings when the program run is too short
• add vmprof.is_enabled/vmprof.get_profile_path
• Pull request (only needed symbols), do not log function names that are not in the profile
• Better descriptor checks (e.g. cannot give a non writable fd to vmprof.enable)
• Warn user if vmprof file is bigger than 100 MB and uploaded to vmprof.com (might be rejected)
• Source distribution includes dwarf.def and other files required to build
• osx: dlopen+dlsym not used for libunwind (use standard way to link to libunwind)