Create a new name for the "custom v2ray-core fork" used by Exclave

- Exclave historically claims itself as using a "custom v2ray-core fork", although the custom v2ray-core fork has long been diverted from the original project for a long time and has been de facto a separate project (like the relationship between v2ray-core and Xray-core). It lacks a unique name though. I have been wanting to give it a new name for a long time, but I have not taken action yet. - I have no interest in merging the recent code changes by v2ray-core. They always add tons of half-baked features and leave them there and never finish them. They always add features without even basic local testing. - By renaming the v2ray-core fork used by Exclave, I don't want Exclave to be considered using v2ray-core anymore. This is a matter of attitude. The renaming does not mean there will be many new features added and should not affect user experience. Code changes from v2ray-core and other similar projects will still be selectively cherry-picked.