Publish a Windows setup beside the AppImage and the disk image

The releases page had nothing for Windows, so the only way in was a
checkout, a Python and a pip install. What goes out now is one setup
program per release: PyInstaller's directory, the pinned ffmpeg the
disk image already uses, and Inno Setup around both. It installs for
the account alone, so no administrator is asked for.

Two executables over the one program there, because a windowed one on
Windows has no standard output at all: Dikte.exe for the Start Menu and
dikte.exe for the terminal, sharing everything they carry. The icon is
drawn by Dikte itself into an .ico, the way the Mac's .icns and Linux's
PNGs already are, so there is still no image file in the repository.

Starting at sign-in is a registry value rather than a Startup shortcut,
which is what lets the setup program, the uninstaller and
`dikte integrate` all mean the same thing: the wizard asks once, and
typing the command changes the answer later.

The three builds move into build.yml, which release.yml now calls
instead of holding its own copy, and which a pull request touching the
packaging runs on its own. A broken build is then a red pull request
rather than a failed release.

packaging/entry.py

@@ -1,11 +1,12 @@
-"""What the AppImage and the disk image start.
+"""What the AppImage, the disk image and the Windows setup 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.
+exits over, and no one clicking an icon would ever find out why. Nothing else
+here is one platform's: the same file is both Windows executables as well.
 
 The three environment lines have to run before anything starts a process,
 opens a connection or reaches for ffmpeg, and before is easier to be sure of