Release 1.6

This release brings several improvements to table-generator:

• table-generator now rounds measurement values in a scientifically correct way,
  i.e., with a fixed number of significant digits, not with a fixed number of decimal places.
  The attribute numberOfDigits of <column> tags in table-definition files
  now also specifies significant digits, not decimal places.
  By default, in HTML tables all fractional values are now rounded (e.g., time measurements)
  and all integer values continue without rounding (e.g., memory measurements),
  previously only "time" columns were rounded.
  The remaining rounding-related behavior stays unchanged:
  In CSV tables, values are not rounded by default,
  and if numberOfDigits is explicitly given for a column,
  it's value will always be rounded in both HTML and CSV tables.
• table-generator now automatically extracts units from the cells in a column
  and puts them into the table header.
• In HTML tables, numeric values are now aligned at the decimal point,
  and text values are left aligned (previously both were right aligned).
• table-generator now allows to convert values from one unit into another.
  So far this is only implemented for values that do not have a unit attached to them,
  and both the target unit and the scale factor need to be specified explicitly
  in the <column> tag.
  This can be used for example to show memory measurements in MB instead of Bytes in tables.
• table-generator now allows columns with links to arbitrary files to be added to tables.
• table-generator does not handle columns where cells have differing units wrongly anymore.
  Previously, the unit was simply dropped, leading to wrong values for statistics.
  Now such columns are treated as text and no statistics are generated.
  (Note that BenchExec never creates such columns by itself,
  only if values are extracted from the tool output this could happen).

Other changes:

• The behavior of benchexec --timelimit was changed slightly,
  if a value for hardtimelimit was given in the benchmark-definition file.
  If a time limit is specified on the command line, this now overrides both soft and hard time limit.
• Implementation of tool-info modules got easier because the test_tool_info helper got improved
  (it now allows to test the function for extracting results from tool outputs).
• Several tool-info modules of tools participating in SV-COMP got improved.
• Simplified cgroups setup for systemd systems.
• Improved documentation.