[BioPython] Bio.Medline parser

[Michiel de Hoon]

> Maybe it would make sense just to describe
> the keys in the docstring, and that would be enough.

OK I'll go with just the docstring for now. If users ask for it, we can add a more descriptive function later.
> 
> Maybe we can just deprecate Bio.Medline (i.e. the
> plain text parser) in favour of Bio.Entrez (and its XML parser)?

Usually I am in favor of deprecating modules if their usefulness is not clear. In this case, however, Medline is a major database, the Medline record format is readily available from NCBI, it is human readable (more or less) and computer readable, the resulting Bio.Medline.Record may be easier to deal with than the record created from XML by Bio.Entrez, and the parser is straightforward but not entirely trivial. Being able to parse such a file is something I'd expect from Biopython.

--Michiel