…::getDefaultSchema() when using a Postgresql database

* Create Expression object + interface
* Refactor Predicates to Predicate Expression
* Formalized specification in Zend\Db\Sql
* cleaned TableGateway API

* Created AbstractSql
* cleaned up join internal implementation

* Fixed PDO Connection with sqlite
* Added a merge to the ParameterContainer
* Delete, Insert, Update now extends AbstractSql, uses shared implementation
* Created Sql factory, to be used as a dependency in TableGateway
* renamed "database" to "scheme" in a dozen places
* Cleaned up unit tests for refactoring

* Added selectWith() to TableGateway

* Cleaned up SelectTest, added testdox, split out where() test
* Added getPredicates() to PredicateSet
* Removed dead code in Where
* Fixed multiple predicate support in Select::where()

Conflicts:
	library/Zend/Db/Sql/Predicate/Literal.php

Fixed unit tests, cleaned up TableGateway's __clone() and fixed statement issue in Update SQL.

…o feature/db-story-41

… improved test

Cleaned up various components for coding standards, better commenting.