add nullptr in binder, 'binder() << nullptr'

Adds a section about execute_all.

Merge pull request #46 from iwongu/extension

Extension

Update version number definitions.

Merge pull request #36 from iwongu/backup

Supports backup methods in database class.

Make dtors not throw exceptions. (src dir).

Make dtors not throw exceptions.

Adds more database methods.

Checks return code before nullifying db pointer.

Add version numbers.