v2.1.0

• New ActiveRecord cache system.
• Added conditions and conditions_args getters to Query.
• Added the parent_model property to Model instances.
• Added the unprefixed_name getter to Table.
• The MODEL_ID constant can be used by ActiveRecord subclasses to define their model id, instead of passing it during __construct.
• Query::joins is now an alias to Query::join.
• Queries can be used as filter argument.
• Queries can be used with Query::join.
• Added alias, mode and on options to Query::join.
• Replaced ActiveRecordException with an Exception interface which is implemented by all the exceptions defined by the package.
• Added install(), uninstall() and is_installed() to Models.
• Added pairs getter to Statement.
• Query::delete() can be used with join().
• Refactored relations.
• Using PSR-4