tools/pipbot: Refactor help and welcome text

Issue #186.
tools/pipbot: Untabify source
tools/pipbot: Add an interactive REPL

If we invoke pipbot with no arguments, start a REPL session.

Issue #186.
tools/pipbot: Set a global REPL

Issue #186.
tools/pipbot: Don't print logo when in REPL

Issue #186.
tools/pipbot: Print welcome text on REPL

Issue #186.
tools/pipbot: Fix REPL argv assignment

Issue #186.
pipbot: Exit with process_command() return code

Issue #186.
Merge branch 'feature/186'
tools/pipbot: Fail gracefully if no JSON files

Print a meaningfyl error if the JSON configuration files aren't found.

Issue #178.