Updater for Path of Building
Update.exe: This is used by the update system to update the runtime binaries.
It runs with administrator privileges to comply with Windows' UAC; that shouldn't be
required on other OSes. It contains a Lua interpreter which runs the script passed as
the first argument. In practice, the only script it will run is UpdateApply.lua.
To allow the LuaJIT binary to be updated, it uses a standard Lua interpreter (not the
JIT) which is embedded in the executable. The script's environment consists of the
standard Lua libraries, plus an extra API function SpawnProcess that starts the given
process and returns without waiting for the process to finish. It also lowers the
execution level so that the new process doesn't run with administrator privileges.
UpdateApply.lua uses this to restart the main application after the runtime files have
been updated.