Compatible with Drupal 6.x

How to setup / use:
- Copy obopac directory to modules (eg. sites/all/modules, sites/default/modules)
- Enable 'OpenBiblio OPAC' module
- Configure from Administer -> OPAC Settings
- Enable 'OPAC Search' block, done.
- Search with keywords:
  * Space (eg. a b, a b c) results books which match least one keyword.
  * OR (eg. a OR b) results as same as space words.
  * AND (eg. a AND b) results books which match both sides keywords.
  * NOT (eg. NOT c) results any books which not match following keyword.
  * For complex keywords, search would be parse from left to right.
