Throwing PacmanConfigurationException instead of IOException.

Since we assume proper configuration, we the exception
extends run time exception.
Used dedicated PacmanConfigurationException.
Merge pull request #28 from SERG-Delft/exception-handling

Exception handling
Bumping to v 6.0.0
Merge pull request #29 from avandeursen/release-600

Bumping to v 6.0.0