Added composer example.

	modified:   site_make.example.yml
Added check for projects directory.

  Moved subtree commands into own function to make drush_site_make easier to
  read/understand.

	modified:   site_make.drush.inc
Updated _site_make_get_info. Tidies up drush_site_make().

	modified:   site_make.drush.inc
README.md