Add possibility of more memory-efficient processing

Use iterators/generators.
Preserve backward compatibility.
Employ iterators/generators for mBank

Memory efficiency improved significantly (checked by memory_profiler-0.31)
Employ iterators/generators for Fio
Employ iterators/generators for Unicredit
Employ iterators/generators for Zuno
Employ iterators/generators for SlSp
Finalize transition to iterators/generators
Merge pull request #5 from xkollar/memprofile

Memprofile