Fix post deploy so failures cause a deploy failure

There was an error generating the cronjob that would have been
highlighted if we failed the script when any of the commands failed.
Exit immediately if a start or end date is passed

Realtime data cannot be backfilled because it is not available from the
GA API
Extend documentation in README

Add more details in README, including a reminder to update the
tokens files. Also document the start-date parameter.
Merge pull request #65 from alphagov/chore/update-README

Extend documentation in README
Merge pull request #64 from alphagov/error-when-backfilling-realtime

Exit immediately if a start or end date is passed
Merge pull request #63 from alphagov/correct-exitcode-for-post-deploy

Fix post deploy so failures cause a deploy failure
Use logging.basicConfig when logging to console

This fixes the 'No handlers could be found for logger "apiclient.discovery"' problem.
Merge pull request #66 from alphagov/fix-console-logging

Use logging.basicConfig when logging to console
Update README with details of start and end dates

If you specify a start date you must also specify an end date.
In addition, the option should be --start not --start-date.
Make post deploy hook use bash

pipefail is not recognised by sh
Merge pull request #67 from alphagov/chore/update-README

Update README with details of start and end dates
Merge pull request #68 from alphagov/make-post-deploy-use-bash

Make post deploy hook use bash