Merge pull request #111 from mackross/master

Update YapDatabase podspec version to 2.5.0
Bug fix for crash caused by YapDatabaseView - getSectionChanges:rowChanges:::. Bug recreated by removing all items from the database, and using mappings with a flexible range.
Bug fix for crash caused by YapDatabaseView - getSectionChanges:rowChanges:::. Bug recreated by removing all items from a view group, and using mappings with a flexible range. Corresponding unit test added.
Bug fix: Invoking [YapDatabaseViewMappings updateWithTransaction] (rather than going through getSectionChanges:rowChanges:::) did not result in properly updating rangeOptions. Several unit tests added.
Bug fix: Pragma auto_vacuum may not have been set properly if a previous database file was auto deleted or renamed due to corruption. Thanks analyzer.
Removed some unnecessary code (dead stores), left over from previous refactoring.
Fixing minor typo - caused view changeset to be generated unnecessarily (but without other harm).
Several minor performance improvements for getSectionChanges:rowChanges:forNotifications:withMappings:
Bumping version in podspec
More logging and help for common exception.
Moving documentation into the *.m files for YapDatabaseExtension protocol.
Improving documentation for extensions protocol.
Performance optimization for YapCache
Bug fix: checkpoint queue was implicitly retaining self
Adding ability to run VACUUM command (synchronously or asynchronously)
Bug fix: flushMemory operation should be asynchronous, so as not to block the main thread. Fixes issue #113
Bumping version in podspec
Adding ability to fetch "pragma auto_vacuum" value. This helps for those who need to run vacuum in order to fix older databases.
Bug fix for rolling back an in-memory view.
Adding convenience method: [YapDatabaseView isEmptyGroup:]