Allow package to be installed anywhere and still find non-Lua assets

packages/sile-logos/init.lua

@@ -3,6 +3,11 @@ local base = require("packages.base")
 local package = pl.class(base)
 package._name = "sile-logos"
 
+local function script_path ()
+   local str = debug.getinfo(2, "S").source:sub(2)
+   return str:match("(.*/)")
+end
+
 function package:_init ()
 	base._init(self)
 end
@@ -13,7 +18,7 @@ function package:registerCommands ()
 	-- registered using \define{} macros in the SIL input format. They should
 	-- probably be refactored using Lua, but to get the party started with SILE
 	-- v0.13 package support we'll just process them here.
-	SILE.processFile("packages/sile-logos/macros.sil")
+	SILE.processFile(script_path() .. "macros.sil")
 end
 
 return package