Vendor the Shockolate engine and build it via a Docker image with every

dependency (SDL2, SDL2_mixer, fluidsynth-lite, a MIDI soundfont)
prebuilt, so compiling the engine needs no network access - just the
image and the engine source. Add res/assets/extract_assets.sh to pull
the game's data files out of a purchased GOG installer, and a Makefile
that assembles a runnable dist/ from the two.

Also add `make package`, which builds a redistributable tarball that
omits the proprietary game assets (shipping res/GET_ASSETS.txt instead)
plus license information for both the MIT tooling and the GPLv3 engine,
and a Gitea Actions workflow that builds and publishes it to
dl.ladkau.de on every push.

engine/appveyor.yml

@@ -0,0 +1,94 @@
+# Shockolate AppVeyor configuration 
+# YAML format reference: https://www.appveyor.com/docs/appveyor-yml/
+
+# This determines the disk image AppVeyor uses while building
+# Despite its name, this image actually contains all sorts of non-VC goodies
+# See https://www.appveyor.com/docs/build-environment/ for all the details
+image: Visual Studio 2015
+
+# Tell build_windows.sh that we're building for AppVeyor
+environment:
+  APPVEYOR: TRUE
+
+platform:
+  - x64
+  - x86
+  
+# Avoid rebuilding external dependencies (ie. SDL and SDL_mixer)
+# Uncache build_ext if external deps change
+cache:
+  - res/music.sf2
+  - build_ext  
+
+# Set up environment variable values for 32 and 64 bit builds
+
+for:
+  -
+    matrix:
+      only:
+        - platform: x86
+    before_build:
+      - set BUILD_SCRIPT=build_win32.sh
+      - set ARTIFACT=systemshock-x86.zip
+      - set MINGW_PATH=C:\mingw-w64\i686-6.3.0-posix-dwarf-rt_v5-rev1\mingw32\bin\
+      - copy CMakeLists.32bit.txt CMakeLists.txt
+  -
+    matrix:
+      only:
+        - platform: x64
+    before_build:
+      - set BUILD_SCRIPT=build_win64.sh
+      - set ARTIFACT=systemshock-x64.zip
+      - set MINGW_PATH=C:\mingw-w64\x86_64-7.3.0-posix-seh-rt_v5-rev0\mingw64\bin\
+   
+# Actual build script..
+# Step 1: Git has to reside in a path without spaces because the SDL build script is weird like that.
+#         So we create a symlink to the real Git, remove it from PATH and add our own.
+# Step 2: We need to use our own make.exe to build stuff, so we add that
+# Step 3: Do the actual building
+
+build_script:
+  - mklink /D c:\git "C:\Program Files\Git"
+  - set PATH=%PATH:C:\Program Files (x86)\Git\bin;=%
+  - set PATH=c:\git\usr\bin;%PATH%;%MINGW_PATH%
+  - copy windows\make.exe \git\usr\bin
+  - set CMAKE_MAKE_PROGRAM=c:\git\usr\bin\make.exe
+  - sh %BUILD_SCRIPT%
+  - build.bat
+
+
+# For now, we don't have any automatic tests to run
+test: off
+
+# Once building is done, we gather all the necessary DLL files and build our ZIP file.
+after_build:
+  - copy %MINGW_PATH%\libgcc*.dll .
+  - copy %MINGW_PATH%\libstd*.dll .
+  - copy %MINGW_PATH%\libwinpthread-1.dll .
+  - copy build_ext\built_sdl\bin\SDL*.dll .
+  - copy build_ext\built_sdl_mixer\bin\SDL*.dll .
+  - copy build_ext\built_glew\lib\glew32.dll .
+  - copy build_ext\fluidsynth-lite\src\libfluidsynth.dll .
+  - 7z a %ARTIFACT% systemshock.exe *.dll shaders/ res/
+
+artifacts:
+  - path: systemshock-x86.zip
+    name: Shockolate (32bit)
+  - path: systemshock-x64.zip
+    name: Shockolate (64bit)
+
+version: '0.5.{build}'
+
+# Finally, we deploy the ZIP file as a GitHub release
+# FIXME: How do we want to be building releases? Seems like this would be better as a manual process
+# TODO: invent a better versioning scheme for the tag name
+
+deploy:
+  - provider: GitHub
+    release: $(appveyor_repo_tag_name)
+    description: 'Latest release build of Shockolate'
+    artifact: systemshock-x86.zip, systemshock-x64.zip
+    auth_token:
+      secure: P1kIk8rRxKAYHqDrOWf0Zf5spfR+N86E0lO8VBu99vHtECJgPLn/Z6tBmL9cxPah  
+    on:
+      APPVEYOR_REPO_TAG: true