Validate the SSH public key file before attempting to add it.
Refactor Git commands into a new GitHelper.
Add some functional tests for GitHelper.
Cleanup
Allow toolstacks to write to $output and use shell abstractions.
Merge pull request #174 from pjcdawkins/validate-ssh-key

Validate the SSH public key file
Make toolstack detection error less scary - addresses #173
Fix double error output from shell commands.
Merge pull request #167 from pjcdawkins/git-helper

Refactor Git/shell/Drush commands; and let toolstacks write output
Update tests now that ShellHelper throws a generic exception.
Don't symlink settings.php; copy and warn.
Merge pull request #176 from pjcdawkins/issue/175/settings-php-symlink

Don't symlink settings.php; copy and warn.
Accommodate multiple details in Platform.sh API errors.
Fix: flags (e.g. --yes) not getting passed to Drush make.
Increase timeout for shell commands.
Prevent writing config multiple times.
Remove responseClass from service descriptions.
Warn the user that the CLI does not run build/deploy hooks.
Merge pull request #178 from pjcdawkins/warn-about-hooks

Warn the user that the CLI does not run build/deploy hooks
Add getProperties() and other useful methods to HalResource.