* Store EIEIO objects using EmacSQL

Store uniform [[https://www.gnu.org/software/emacs/manual/html_node/eieio/index.html][EIEIO]] objects in an [[https://github.com/skeeto/emacsql][EmacSQL]] database.  [[https://www.sqlite.org][SQLite]] is used
as backend.  This library imposes some restrictions on what kind of
objects can be stored; it isn't intended to store arbitrary objects.
All objects have to share a common superclass and subclasses cannot
add any additional instance slots.

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#+html: <a href="https://github.com/magit/closql/actions/workflows/compile.yml"><img alt="Compile" src="https://github.com/magit/closql/actions/workflows/compile.yml/badge.svg"/></a>
#+html: <a href="https://stable.melpa.org/#/closql"><img alt="MELPA Stable" src="https://stable.melpa.org/packages/closql-badge.svg"/></a>
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