change drupal_bootstrap() to use a Pimple container.

drupal_bootstrap() sets up the Drupal run time environment with all of
its parameters and services. This function is response for PHP and
environment settings, sessions, locale, database, page cache, page
headers, Drupal site variables and more.

drupal_bootstrap() wants to be failsafe, but as a result of all these
responsibilities, it is very complicated and full of interdependencies.
Changing this function to use a Pimple container will let the bootstrap
process be extended, overridden and rewritten.
Support autoloading in Drush.

This only works from the composer.json and vendor directory in the
Drupal root.
move functions from included file to Pimple container.

This moves all the bootstrap phase function bodies into the Pimple container. Since these functions are not to be called outside of bootstrap, this should have no side effects.

Large phases with different things happening are separated but still called from within the original bootstrap phase.
add autoload script to test runner.