invalid flow number now leads to exit_failure
Moved sanity checks in separate function.
Removed bug in rate parsing
strcpy() to uninitialized address, replaced by strdup()
Moved rate option parsing into separate function
Moved host option parsing into separate function
[Code Style] Fixed some unnecessary linebreaks
Merge pull request #91 from erzb5e6f65/cleanup_optionparser

Cleanup optionparser