bootstrap: generate doom2.wad

A trivial program to regenerate the doom2.wad "blob", needed to
bootstrap deutex and prevent it from leaking material from any
existing iwad into a new build, as described in bootstrap/README.txt.

This should address bug #67 (Fabian Greffrath)

bootstrap/bootstrap.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+import sys
+import struct
+
+def main():
+    # read PLAYPAL from stdin, write minimal doom2.wad to stdout
+    if sys.stdin.isatty():
+        print("Usage: %s < playpal.lmp > doom2.wad" % sys.argv[0],
+                file=sys.stderr)
+        sys.exit(1)
+
+    # three lumps needed - see bootstrap/README.txt
+    lumps = [(b'PLAYPAL',  sys.stdin.buffer.read()),
+             (b'TEXTURE1', struct.pack("i", 0)), # empty texture1
+             (b'PNAMES',   struct.pack("i8s", 1, b''))] # single pname
+
+    # calculate wad directory (lump offsets etc.)
+    pos = 12
+    waddir = []
+    for name, data in lumps:
+        waddir.append((pos, len(data), name))
+        pos += len(data)
+
+    # write wad header
+    wadheader = (b'IWAD', len(waddir), pos)
+    sys.stdout.buffer.write(struct.pack("4sii", *wadheader))
+
+    # write lump contents
+    for name, data in lumps:
+        sys.stdout.buffer.write(data)
+
+    # write wad directory
+    for i in waddir:
+        sys.stdout.buffer.write(struct.pack("ii8s", *i))
+
+if __name__ == "__main__": main()