Add flexible window management.

New customization group: Ebib Windows
New customization options: ebib-popup-entry-window, ebib-display-entry-buffer-on-startup
New function: ebib-pop-to-buffer (plus action functions)
Honour ebib-popup-entry-window in ebib-quit-log-buffer.
Adjust behaviour of [return] in index buffer.

If `ebib-display-entry-buffer-on-startup' is unset, [return] now also
displays the entry buffer and switches to it.
Make [return] not switch to entry buffer.

[return] now just shows the current entry, but does not switch to the entry buffer.

Also modify the behavior of `ebib-lower': if
`ebib-display-entry-buffer-on-startup' is not set, it switches to another
window and checks if that happens to be an Ebib window. If it is, switch to
another buffer.
Change link info on package management in Emacs 23

Since Wikemacs is shutting down, change reference to emacswiki.org.
Do not delete other windows when not displaying entry buffer on startup.
Fix doc string of `ebib-setup-windows'.
Collapse ebib-layout and ebib-display-entry-buffer-on-startup
Properly restore dedicated status in `ebib-with-window-nondedicated'.
Temporarily make window non-dedicated when leaving the strings buffer.

If `ebib-layout' is set to `custom', a dedicated strings window means we
can't switch back to the entry buffer in the same window.
Add norecord=t and same-window=t to switch-to-buffer calls.
Wrap switch-to-buffer in ebib-quit-log-buffer in ebib-with-window-nondedicated.
Rebind `C-x b' and `C-x k' in entry, strings and log buffers so that they leave the buffer.
Update doc strings of `ebib-layout' and `ebib-popup-entry-window'.
Add texinfo output of Pandoc to .gitignore.
Add echo statements to pre-commit.sh
Update manual with window management options.