Run Clang-tidy across codebase.
make lpc socket closeonexec, set send buffer size.

Fix #225
Remove unused runner.cc
Implement million second level gametick loop.

Part of #203, also deleted HEARTBEAT_INTERVAL in options.h
Add two runtime config, gametick msec / heartbeat interval msec.
Adding add_walltime_event, rename add_tick_event to add_game_tickevent.

part of #202
Adding call_out_walltime() efun for walltime delay based callback.

Fix #202.
Accepting float argument for call_out and call_out_walltime.

Allow subsecond scheduling (gametick or millisecond resolution) for call_out.
Fix #203.
Use time_to_gametick / gametick_to_time to simplify code.
Fix compile under m32.
Merge pull request #226 from sunyc/master

Fixed-delay game tick scheduling & call_out_walltime & subsecond call_out