Bio.SVDSuperimposer cleanup to remove nested module name

[peterjc]

This was prompted by having to fix an import * in this area of the code, and the recollection of epydoc complaining about the class and sub-module name clashing (one shadows the other making imports confusing).

This pull request essentially moves the code in Bio/SVDSuperimposer/SVDSuperimposer.py into Bio/SVDSuperimposer/__init__.py from where is was typically imported anyway.

As explained in the DEPRECATED file, this could break some existing code doing long-winded imports, but the standard import is not affected (and probably most users import it via Bio.PDB anyway and won't be affected at all).

[etal]

Looks good to me. Relatedly, a line in test_SVDSuperimposer.py can be safely changed from:

from Bio.SVDSuperimposer import *

to:

from Bio.SVDSuperimposer import SVDSuperimposer

because the only contents of the module are the SVDSuperimposer class and a *-full of numpy imports, which are already separately imported into the test script.

[peterjc]

Rebased & applied, plus the import fix suggested by Eric on the mailing list:
c8dfe46