fixed overwriting of existing export. still not working: export - import
- export again. TODO: free resources
trying to fix the 2nd export problem: added lock variable which
separates delete process from export, closed everything in DBExchanger.
Still not working...
fixed overwriting error by implementing proper database shutdown.
still not working on windows. made sure that all streams are closed.
Fixed windows import/export problem.
added control mechanism, now it's not possible to delete directories
containing more files than the usual database files
Created own logger class
started to integrate error logging in main class
increased version: 0.1.4
Merge pull request #2 from random-access/patching

version: 0.1.4 
- patched import / export
- added logging