elPrep5.1.0 release

Binaries can be downloaded here:
https://www.imec-int.com/en/expertise/lifesciences/genomics/dna-sequence-analysis-software

Update to the sfm command:

Added merging of headers when using the sfm command with a directory
containing multiple files as input.

The merging respects the requirements outlined in the SAM spec:

• order of sequence dictionaries is kept
• read group identifiers are made unique if needed + optional rg tags of
  reads are updated accordingly
• program line identifiers are made unique if needed + optional pg tags
  of reads are updated accordingly
• comment lines are merged
• the sorting order is set to Unknown

If elprep cannot merge while guaranteeing the above constraints, an
error is produced.