gnureadline, no package

- extension is now _gnureadline
- gnureadline.py imports _gnureadline and sets sys.modules['readline']  = _gnureadline
don't explicitly set `sys.modules['readline']`

- gnureadline.so is the extension
- readline.py imports from gnureadline
Merge pull request #27 from minrk/gnureadline

gnureadline, no package

- gnureadline.so is the extension
- readline.py imports from gnureadline
- don't explicitly set sys.modules['readline']