Implement batch mode of the REPL

[omasanori]

Batch mode reads code from standard input as the current interactive REPL does, but does not print prompts. It is useful to execute an expression passed from a pipe, or to input code using here-documents.

When standard input is terminal (you can detect it with isatty), interactive mode should be selected. Otherwise, batch mode seems better. It is great if command line options to override the default are provided.

[KeenS]

Done in #226