Deprecating Bio.PDB.Dice

Hello all,

This came up in discussion on GitHub issue #820 [*] about turning
existing self-tests into proper unit tests for user under TravisCI etc.

Bio/PDB/Dice.py is essentially an example of how to write your
own selector for use with PDBIO to write a subset of a PDB file.

We are proposing to formally deprecate Bio.PDB.Dice (and later
remove it [**]), and ideally reuse this as an example script and/or
test case.

If anyone is using the Dice module, please let us know.

Thank you,

Peter

[*] https://github.com/biopython/biopython/issues/820
[**] http://biopython.org/wiki/Deprecation_policy