Added some tests/examples

Examples include:
- how to specify multiple chains
- complexes to be numbered against different references
  - a homology model of the mammalian nmda receptor
- take care of ligand/solvent renumbering
  - 3KG2
- renumber a polymer that is represented by different chains in the pdb file
  - 1JEN, also includes a modified amino acid and how to cater for this
- renumbering with standard non-standard amino-acids, like selenomethionine
  - 2FHB