Add logging support to package

Add support for the Python logging package, with separate loggers
for each submodule.

Use this new logging support to attempt to complain when IP
address conversion fails in _whereis, rather than simply giving up.
Import the submodules in __init__.py

Import the submodules, so that people using the package don't
have to import afs and then afs.fs, because that's just dumb
Update docstrings for Cython functions

Update the docstring for whichcell, because its signature can't
be determine by introspection, and it's exported into afs.fs.

Correct typo in docstring for _lsmount
Stop exporting __all__ and stop importing whichcell

Don't import anything from afs._fs into afs.fs; instead provide
a higher-level whichcell which returns None when the path is not
in AFS (rather than throwing OSError).  Rename the calls to
_fs functions as appropriate.
Add examine and whereis high-level functions

Add high-level functions for "fs examine" and "fs whereis".
Add a convenience function for DNS lookups.
Add logging to afs.fs
Use sizeof() in pioctl_write()

Don't assume that outbuffer is AFS_PIOCTL_MAXSIZE, just call
sizeof() and let the lower layer deal.
Drop support for python < 2.6

Require Python 2.6 in setup.py and remove the last vestiges of 2.5
exception syntax.
Release a new upstream version

Be bold and release version 0.2.0