setup.py: Don't error if README.txt exists, just don't write it.

This caused a problem on pypi installation. This also meant we
had to upload 0.8.1 there instead of 0.8.
elpy-shell-send-region-or-buffer: Pass arguments to python-shell-send-region

That function requires BEG and END arguments, so tell it about
the region.
elpy.rpc, elpy.server: Create and use a handle method for unknown methods

This means we do not have to define every single method defined by
the backends twice, in server.py and native.py. The design mirrors
the standard XML-RPC server design.
Pydoc completion: New feature.

This commit adds the ability to `elpy-doc` to complete, using ido,
the available Python packages, modules, and classes. Using
`C-u C-c C-d` will now prompt for the symbol at point and allow
completion, using . to look inside a package.