Implement CSV / TSV import (#45)

- add csv/tsv importer
- add `make_map` script function
- add `alt name` field property
- add `construction script` field property
- add `construction script` game property

doc/function/index.txt

@@ -11,6 +11,7 @@ These functions are built into the program, other [[type:function]]s can be defi
 | [[fun:to_color]]		Convert any value to a [[type:color]]
 | [[fun:to_image]]		Convert any value to an [[type:image]]
 | [[fun:to_date]]		Convert any value to a [[type:date]]
+| [[fun:make_map]]		Create a [[type:map]] from two [[type:list]]s
 | [[fun:type_name]]		Get the type of a value
 	
 ! Numbers			<<<