Implemented calculation of unique crystal contacts
Now hetatoms can be filtered by size when calculating ASAs in interfaces
Improved HETATOMs filtering for interface ASA calculation
Some refactoring and improvement of docs
Added unit test for CrystalBuilder and fixed some docs
Introduced a more general interface-between-2-molecules representation
Now ChainInterface/List became StructureInterface/List and are moved to
contacts package. Other kind of interfaces between 2 molecules or
submolecules (e.g. between domains) can be handled with this
representation.
Merge pull request #158 from josemduarte/master

New feature: reconstruction of crystal from AU and calculation of unique interfaces in crystal