csv-parser

Feature/buffered writer (#147)

* Added a new template parameter 'Flush' (bool) to the DelimWriter class. If set to true the class will work as before (flush after every function that writes some data). However if you set it to false, these flush calls will be skipped which improves the execution time.
Also added a destructor (will simply flush) and a flush function.
The functions make_csv_writer_buffered and make_tsv_writer_buffered were also added.
In csv_reader.cpp replaced the std::endl in the loop with a simple '\n', added a flush after the loop finished.

* Formatting and some more docu on the DelimWriter class.

Co-authored-by: Lukas Kerkemeier <kerkemei@campus.uni-paderborn.de>