v.0.3.1

New features

• New function - delink(). Unlink identifiers.
• New function - episodes_wf_splits(). Wrapper function of
  episodes() for better optimised handling of duplicates records.
• New function - combi(). Numeric codes for unique combination of
  vectors.
• New function - attr_eval(). Recursive evaluation of a function on
  each attribute of a sub_criteria.

Changes

• Two new case_nm values - Case_CR and Recurrence_CR which are
  Case and Recurrence without a sub-criteria match.

Bug fixes

• Corrected length arrows in schema.epid.
• Corrected outcome of eval_sub_criteria with 1 result.