Rename `read-intern-literal' to `datum-intern-literal'. Interning is needed only in `read-syntax' or `datum->syntax' to set up the invariants that the bytecode compiler needs for cross-module optimization. When `read'ing numbers from a data file, meanwhile, interning slows things down a lot and doesn't seem worthwhile.
This change saves a small amount of space in cross-reference files and some space in loaded cross-reference information. It also saves work converting strings to mutable on deserialize, although the performance difference seems negligible.
and improve docs for `scribble/decode'