A fix for the write() function.
Fix for the unit test for writing an amino acid sequence.
Added the missing import of the spin_loop() function.
Added the missing import of the open_write_file() function.
Wrote the count_spins() function.
Added the import for the count_spins() function.
Fixes for the write() function.
The display() function now works (although not fully).
Removed the import of the now non-existant Sequence class.
Converted the load_PDB_sequence() class method to a module function.