kcptun-libev v2.3.4

Changes since v2.3.3:

1. [server] Replace address faster in rendezvous mode.
2. [conf] Migrate to json-c.
3. [contrib] Sync upstream changes.

NOTE: New runtime dependency is introduced in this release.

Build variants:

• -static: does not require the system to support dynamic linking.
• android, win32: requires only the dynamic libraries provided by the system.
• other: runtime dependencies should be installed.

Full Changelog: v2.3.3...v2.3.4