Begin using a SQL Stored Procedure API to the data.

That simplifies the frontend a lot and allows for easier debugging,
where running the same query in a psql console is made easy.
Fix useless warning about non-executable files.

Better would be to find the executable name in the PATH when it's not an
absolute pathname, but for now just get rid of a useless check.
Implement some more of the PL SQL API.

Also issue a message when an animal wants to pick a job from an empty queue.
Review the Makefile, add INSTALL documentation.

It appears to be harder than it should to build pginstall, this patch is
an attempt at simplifying the process by reviewing the Makefile, adding
an effective `make clean` command for getting out of a confusing
situation.

Also, provide an INSTALL.md file covering the basics and dependencies
you need to manually care about when you want to build pginstall
yourself.
Fix archive-filename function name...

Each function better have its very own unique name within its package,
and we had a clash with the dao objects.
Review the model and the SQL API.

The whole model is now installed into the pginstall schema, and the SQL
API contains some more functions. The whole queue management API for
extensions should now be available as SQL level function calls, allowing
for easier debugging of some strange situations.

An improved SQL file reader is provided to be able to "parse" the
dollar-quoted function bodies and manage loading the whole model and API
from the lisp code directly.
Assorted frontend fixes.
Small message improvement.