reverting the reorganization done in 3455-3456 in order to make merging my experimental branch to trunk easier.

Preparation for new organization of code in to sub packages. Changed autoload() to work with new structure.

CHG: Added documentation for Doctrine_Pager and Doctrine_Pager_Range* classes
TODO: Finish pagination documentation

ADD: Added methods: addMaskReplacement, removeMaskReplacement and cleanMaskReplacements in Doctrine_Pager_Layout. They are responsable to make masks behavior as another masks or values on predefined situations.

Implemented Doctrine_Pager_Range functionality. This classes enables a powerful way to generate page ranges (Fowler's pattern) to be used coupled with Doctrine_Pager. Already implemented 2 of the most used ranges: Doctrine_Pager_Range_Jumping and Doctrine_Pager_Range_Sliding.