* progress-bar in merge ( if asked for )
* check memory if no memory-limit provided
* check for space on scratch or current-directory
* projects and experiments
* as lib
* maybe 'lmdb' is faster as lookup-table, removes the merge-sorting, and merge-step

problems:
SRR2989969 ( difference in ref-orientation between SEQUENCE- and PRIMARY_ALIGNMENT-table )

test test test
