Allocate an "stdin", "stderr" and "stdout" for languages that read from/print to these streams.

[Balletie]

E.g. the SimpleLanguage has a println function. The stream that this function prints to should be different from the stream that is used for REPL output, so that the user can distinguish the two. Currently it just prints to System.out.

The streams can be injected using the PolyglotEngine.Builder.

Example:

[In    ]: println("Hello World")
[stdout]: "Hello World"
[Out   ]: UnitV()