Exit on EOF (Ctrl-D), interrupt on Ctrl-C.

Changes behavior of EOF (Ctrl-D) and Ctrl-C.

On EOF (Ctrl-D in the repl), exits the repl.

On Ctrl-C, interrupts the program in execution.
This means that Ctrl-C can be used to interrupt a long-running
computation (tested with a js `while (true) ;` on my machine).
Make eof non-error exit code
Merge pull request #17 from maxsnew/eof

Exit on EOF (Ctrl-D), interrupt on Ctrl-C.