Bitcloud.JS: Define exit command for local_repl

[gnostication]

Currently, when bitcloud.js is run, the end result is a repl command-line interface bitcloud>

There is no command to exit. Exiting can be the first command that the repl interface supports.

• Produce and test code to add one or more exit command functionality to the repl interface.
• Document the method of adding the command within the code so that multiple exit command options can be made available, and other commands also easily written.