Some Fixes

[ZzzzzzzSkyward]

For other users:

1. DSSP executable is not available in the provided ftp server. But I can get it using conda install -c salilab dssp, and the command is mkdssp instead of dssp.
2. from Bio._py3k import StringIO should be removed in python3. Without StringIO, the output can be read as str instead of file.
3. without chain_ids defined residues = get_residues(opts["--pdb"], chain_ids=chain_ids) will throw an error. Just add chain_ids=None.

[jinhuili-lab]

Thank you, Others can refer to: https://github.com/jinhuili-lab/PDB2ContactMap

[jinhuili-lab]

If possible, I will re-develop it.