Set up SEGV crash handler in main() not server()

Now all commands will attempt to log a GDB backtrace on a crash, not
just the server daemon process.

Added strbuf_append_signal_name()
Rename TIME_NEVER... to TIME_MS_NEVER...
time_ms_to_timeval()
Improve MSP API: MSP_SOCKET instead of struct msp_sock *
UNFINISHED Improve MSP API documentation