BeginRepl (args) -- the REPL, both interactive and script modes begin here This allows us to prime the global env with ABS_INTERACTIVE = true/false, load the builtin Fns names for the use of command completion, and load the ABS_INIT_FILE into the global env.

Core of the REPL.

support for ABS init file.

support for user config of ABS REPL prompt string.