Fixed use of undefined variable in artemis_color method; docstrings

This was flagged in the https://landscape.io/github/biopython/biopython report.
Fix error message
Rework example to avoid repeated imports
Remove obsolete example.

That old code no longer worked, but perhaps Bio.SeqIO.index(...)
could be used as an alternative approach? It allows you to index
a file and then parse each record within a try/except block,
and thus handle some of the records in the file breaking the
parser.
Avoid mutable default argument
PEP8 white space changes
Avoid import star
Fix another mutable default value