Simplified.

No need to call `cd-absolute`. It's probably better to supply the
DRUPAL_ROOT as a parameter to drush.
Improved `drupal-tail-drupal-debug-txt`.

Added the DRUPAL_ROOT as parameter to the drush command.
Added a `drupal-drush-php-eval`

Evaluate active region with `drush php-eval`.

Idea from @kostajh. Closes #46.