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/src/Libraries/2D/Source/Flat8/fl8clin.c

@@ -0,0 +1,105 @@
+/*
+
+Copyright (C) 2015-2018 Night Dive Studios, LLC.
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+/*
+ * $Source: r:/prj/lib/src/2d/RCS/fl8clin.c $
+ * $Revision: 1.7 $
+ * $Author: kevin $
+ * $Date: 1994/10/17 14:59:57 $
+ *
+ * Routine to draw an rgb shaded line to a flat 8 canvas.
+ *
+ * This file is part of the 2d library.
+ *
+ * $Log: fl8clin.c $
+ * Revision 1.7  1994/10/17  14:59:57  kevin
+ * Use palette macros in preparation for switch to palette globals.
+ *
+ * Revision 1.6  1994/06/11  01:24:08  lmfeeney
+ * guts of the routine moved to fl8{c,s}lin.h, per fill type
+ * line drawers are created by defining macros and including
+ * this file
+ *
+ * Revision 1.5  1994/05/06  18:18:38  lmfeeney
+ * rewritten for greater accuracy and speed
+ *
+ * Revision 1.4  1994/05/01  05:34:38  lmfeeney
+ * rewritten using simple dda algorithm (+ bit twiddle hack) for greater
+ * speed (20/30%) and improvement for e.g. diagonal lines
+ *
+ * Revision 1.3  1993/10/19  09:50:19  kaboom
+ * Replaced #include <grd.h" with new headers split from grd.h.
+ *
+ * Revision 1.2  1993/10/01  15:43:46  kaboom
+ * Pared down include files to reduce dependencies.
+ *
+ * Revision 1.1  1993/07/01  22:11:55  spaz
+ * Initial revision
+ */
+
+#include "cnvdat.h"
+#include "fix.h"
+#include "plytyp.h"
+#include "scrdat.h"
+#include <stdlib.h>
+
+// MLA #pragma off (unreferenced)
+
+#define fix_make_nof(x) fix_make(x, 0x0000)
+#define macro_get_ipal(r, g, b) (long)((r >> 19) & 0x1f) | ((g >> 14) & 0x3e0) | ((b >> 9) & 0x7c00)
+
+#undef macro_plot_rgb
+#define macro_plot_rgb(x, p, i) \
+    do {                        \
+        p[x] = grd_ipal[i];     \
+    } while (0)
+
+void gri_flat8_ucline_norm(long c, long parm, grs_vertex *v0, grs_vertex *v1) {
+#include "fl8clin.h"
+}
+
+#undef macro_plot_rgb
+#define macro_plot_rgb(x, p, i)                        \
+    do {                                               \
+        p[x] = (long)(((uchar *)parm)[(grd_ipal[i])]); \
+    } while (0)
+
+void gri_flat8_ucline_clut(long c, long parm, grs_vertex *v0, grs_vertex *v1) {
+#include "fl8clin.h"
+}
+
+#undef macro_plot_rgb
+#define macro_plot_rgb(x, p, i)      \
+    do {                             \
+        p[x] = p[x] ^ (grd_ipal[i]); \
+    } while (0)
+
+void gri_flat8_ucline_xor(long c, long parm, grs_vertex *v0, grs_vertex *v1) {
+#include "fl8clin.h"
+}
+
+/* punt */
+#undef macro_plot_rgb
+#define macro_plot_rgb(x, p, i)                        \
+    do {                                               \
+        p[x] = (long)(((uchar *)parm)[(grd_ipal[i])]); \
+    } while (0)
+
+void gri_flat8_ucline_blend(long c, long parm, grs_vertex *v0, grs_vertex *v1) {
+#include "fl8clin.h"
+}