Organized Domain class and all its subclasses into a single file, structure.py.
Simplified implementation of classes in structure.py file.
Briefly renamed biology module biology2. Trying to resolve an issue with case sensitivity.
Forgot to delete old files.
Changed the name back to biology again.
Moved the implementation of Module class into structure.py.
Revert "Moved the implementation of Module class into structure.py."

This reverts commit a53ab1682713e5723c63321db443be141a9b5ca9.
Moved the implementation of OpenReadingFrame into structure.py.
Moved implementation of GeneCluster class into structure.py.
Moved implementation of Module class to combinatorics.py file.
Simplified implementation of Module class in combinatorics.py.
Forgot to remove old implementation of Domain class.
Moved implementation of BuildingBlock class into combinatorics.py file.
Moved implementation of AssemblyLine class into combinatorics.py file.
Moved implementation of Substrate class into structure.py file.
Moved implementation of Peptide class into structure.py file.
Moved implementation of Synthesis class into combinatorics.py file.
Merged 'packages' branch into 'master' branch.