Add tuning-related parameters to the command line tools that implement the data format conversions

[hartig]

TODO: what parameters do we have and which of them may be reasonable to expose?

[keski]

The command line tools, ConverterRDF2RDFStar and ConverterRDFStar2RDF, do not support all of the flags that are provided in their respective usage instructions. Not all of these are strictly required, but we should clean it up to avoid any confusion.

[keski]

The main performance issues seems to stem from the fact that the PipedRDFIterator and PipedTriplesStream should not be run in the same thread. Initial tests indicate that fixing this leads to fairly consistent results for both the first and second pass (see below).

For ConverterRDFStar2RDF:

# lines (nested)	First pass	Second pass
200,000	54k rows/s	29k rows/s
500,000	80k rows/s	31k rows/s
1,000,000	102k rows/s	32k rows/s
2,000,000	132k rows/s	32k rows/s

Similar performance improvements were also seen for ConverterRDF2RDFStar for larger files.

[keski]

nested.ttls (150M records) now takes around 2 hours (125 minutes) to convert into reification format on the server using the predefined buffer size (which should probably be set a bit higher).

[keski]

nested-reif.ttl takes a about 1.5 hours (95 minutes) to convert back to TTLS. But comparing this file with the original nested.ttls, however, shows major discrepancies in terms of file size. This seems to be the result of percent encoding (see issue #16).