Build an AppImage and a disk image, and publish them

Installing meant cloning the repository and running a shell script, which
is a fair ask of somebody who already has a terminal open and no ask at
all of anybody else. The releases page now carries an AppImage and a disk
image per Mac architecture: a push to master rebuilds a rolling "latest",
a v* tag publishes a version and leaves it there, and the Run button in
the Actions tab raises the number by running scripts/release.sh, which is
the same script and not a second copy of what it does.

Two things in the application had to give for that. A build has no
__main__.py on disk, and an AppImage is mounted somewhere new every run,
so the command a shortcut is registered with cannot go on being this
interpreter and this file; ipc.launcher() answers with the AppImage or
the bundle instead. And a build carries its own libstdc++, which every
process it starts inherits through LD_LIBRARY_PATH and none of them can
live with: ffmpeg, ydotool and wl-copy are the distribution's binaries
built against the distribution's libraries, and AppImageLauncher, which
is what starting the AppImage again goes through, refuses outright.
integrate.py puts that variable back before anything else runs.

Nothing installs itself over an installation that is already there.
install.sh's menu entry, install-mac.sh's login item and the desktop file
AppImageLauncher writes are each recognised and left alone, so trying a
download once does not quietly move the machine onto it. `dikte
integrate` is how you ask for it outright, and --remove takes it back.

The disk image carries an ffmpeg, pinned and checksummed, because macOS
records through one and ships nothing like it. It is signed ad-hoc and
not with an Apple certificate, so a first launch is refused until Open
Anyway and the permissions are asked for again after each update; both
READMEs and the release notes say so.

packaging/entry.py

@@ -0,0 +1,23 @@
+"""What the AppImage and the disk image start.
+
+dikte/__main__.py is written for a checkout: it puts the directory above the
+package on the import path, which a build has neither the need for nor a
+directory to point at. What is left over is one thing a checkout never sees.
+The Finder hands a double-clicked application a -psn_0_… argument naming the
+process serial number, which argparse reads as a flag it has never heard of and
+exits over, and no one clicking an icon would ever find out why.
+
+The two environment lines have to run before anything starts another process,
+and before is easier to be sure of here than anywhere further in.
+"""
+
+import sys
+
+from dikte import integrate
+from dikte.app import main
+
+if __name__ == "__main__":
+    integrate.restore_library_path()
+    integrate.add_bundled_tools()
+    sys.argv[1:] = [arg for arg in sys.argv[1:] if not arg.startswith("-psn_")]
+    sys.exit(main())