WIP: Unix domain socket binding support

[hugmanrique]

A niche feature, but useful for upper-level proxies running on the same host, e.g. HAProxy (which Velocity already supports). I followed the Redis configuration convention, where the binding address and Unix domain socket address are different options. Mixing both types of sockets under the bind config would complicate determining if the given address is a hostname or a filename.

[astei]

I actually already did this in Velocity 2.0.0: b003890

I'd be fine with you backporting this.

[hugmanrique]

Ughh, I hate myself for not looking on the 2.0 branch. API changes like b003890#diff-9045d615f487de57c8df1f7e008486d03740e5051247b1b9007e8d15f42f2eccL18 are not possible in minor versions, so will have to wait.

[astei]

Fair enough. I will need to find some time to forward-port all the recent Velocity 1.1.x changes to the 2.0.0 branch. At the same time I'm going to try and rein in all the changes planned for 2.0.0.

[8MiYile]

I hope your UNIX Socket method is used for the following configuration
Example:

[servers]
# Configure your servers here. Each key represents the server's name, and the value
# represents the IP address of the server to connect to.
lobby01 = "tcp:127.0.0.1:30066"
lobby02 = "unix:/tmp/mcs-lobby.sock"

In addition, Paper server needs this support or other servers need to load additional plugins and support disabling the original game port