feat(cli): Allow multiple runtime SILE_PATH segments (backport from d…

…evelop branch)

sile.in

@@ -6,7 +6,11 @@ SHARED_LIB_EXT = "@SHARED_LIB_EXT@"
 
 -- At this point at run time we may or may not have anything useful in package.path,
 -- so require() isn't something we can rely on.
-local status = pcall(dofile, "@SILE_PATH@/core/pathsetup.lua")
+local status
+for path in string.gmatch("@SILE_PATH@", "[^;]+") do
+  status = pcall(dofile, path .. "/core/pathsetup.lua")
+  if status then break end
+end
 if not status then
   dofile("./core/pathsetup.lua")
 end