add retrieveData to Tag
removed some redundant code from TestTag
add test for Tag::retrieveData
add retrieveData method to MultiTag
add test for retrieveData on MultiTag
nicer nix-tool --help output
dsiplays only the module options, textual improvements
display of module options, only, text improved
Merge pull request #380 from jgrewe/tag_convenience

Tag convenience - data retrieval directly from the Tag

Looks OK for me. However, I'm not 100% sure whether this is really the right place.
Merge pull request #384 from jgrewe/multi-tag-convenience

Multi tag convenience - retrieve data directly from the multi tag 

LGTM
Merge pull request #385 from jgrewe/nix_tool

Some improvements of the nix-tool help texts

LGTM
NDArray: use data() function to access vector data
NDArray: delegete access with NDSize to size_t arg
NDArray: use memcpy instead of reinterpret_cast
Merge pull request #386 from gicmo/nd_polish

Small NDArray improvements
[test] Benchmark: extract a config data into class
[test] Benchmark: extract Benchmark base class
[test] Benchmark: all tests accept a block now

Plus helper function to open a data array from a cfg.
[test] Benchmark: separate cfg and mark creation
[test] Benchmark: remove unused variable