configure: Re-order string exports
configure: Add a GIT_RESERVED_BRANCHES export

Issue #187.
configure: Reject commits onto the stable branch

Issue #187.
Merge branch 'feature/187'
configure: Alphabetise the list of commands

Issue #178.
tools/pipbot: Add a run_extern() command

Issue #188.
tools/pipbot: Alphabetise pause command
tools/pipbot: Add support for external commands

Commands:

    ./autogen.sh
    autogen
    autogen.sh
    configure
    gitk
    ll
    ls
    make
    pwd

    branch   Git branch
    pull     Git pull
    push     Git push

Issue #188.
Merge branch 'feature/188'