Introduce command 'puppetdb' as a sub-command dispatcher

This patch includes a new base tool named 'puppetdb' thats job for now is
to accept sub-commands and arguments and execute their equivalent
puppetdb-<sub-command> command (if it exists).

This modifies all documentation to use the new syntax, and all acceptance
tests as well.

Signed-off-by: Ken Barber <ken@bob.sh>