+FastString: A compact, hash-consed, representation of character strings.
+ Comparison is O(1), and you can get a Unique from them.
+ Generated by the FSLIT macro
+ Turn into SDoc with Outputable.ftext
+
+LitString: Just a wrapper for the Addr# of a C string (Ptr CChar).
+ Practically no operations
+ Outputing them is fast
+ Generated by the SLIT macro
+ Turn into SDoc with Outputable.ptext
+
+Use LitString unless you want the facilities of FastString