elpy-initialize-variables: Fix some typos

Should add to python-mode-hook, not python-mode. And use locate-library
to find our installation path because, well, load-file etc. are not
bound correctly when this function is run.
elpy-installation-instructions: Remove mention of C-c C-e binding

That keybinding was removed because virtualenv changes don't happen
too often.
elpy-refactor-window-configuration: New variable.

In a refactoring buffer, store the window configuration from when
the refactoring action was started, and restore it when the
operation is committed. This prevents window configurations from
being lost after a refactoring action.

This commit also records point in buffers being changed to
leave it at least somewhat closeby if the content changes.

Fixes #45.
elpy-flymake-python-init: Don't bother creating a relative path.

The logic for creating a relative file actually breaks for heavily
symlinked paths. As there is no need to create a relative path
in the first place, just drop that logic.

Fixes #42.
findundefined: More extensive syntax coverage.

The findundefined library was unable to cope with some syntax
uses employed by Python. This has been fixed. It can now parse
all files in the Python 2.7 standard distribution, which I guess
is sufficient.

Fixes #41.
get-pydoc-documentation: New RPC call.

This returns the Pydoc documentation for a symbol, like calling
pydoc on the command line. This became necessary because virtualenv.el
does not set PATH correctly, so pydoc did not pick up on libraries
within the virtualenv. The change means the auto-completed entries
are actually all findable.

Fixes #44.