update CHANGELOG

CHANGELOG.txt

 Changes in Release 2.2.x
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+ * Add AAindex databases (Kawashima et al., 2000)
  * Removed GUI components in containers
  * DSSP 4.0 support in DSSP binding (https://github.com/PDB-REDO/dssp)
  * mol.alg.PDBize does not turn plain polymer chains (not marked peptide or