The core package uses global variables that keep from having
more than one Tile38 instance runnning in the same process.
Move the core variables in the server.Options type which are
uniquely stated per Server instance.
The build variables are still present in the core package.
This commit cleans up various Go code in the internal directory.
- Ensures comments on exported functions
- Changes all *Server receiver in all files to be "s", instead
of mixed "c", "s", "server", etc.
- Silenced Go warnings for if/else with returns.
- Cleaned up import ordering.
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