[init] Add new initrd format

A new compressed initrd format for srv.init to load drivers, services,
and data from, instead of every file getting loaded by the bootloader.
This will allow for less memory allocated by the bootloader and passed
to init if not every driver or data file is loaded.

Loading, passing, and using the new initrd will be done in a coming
commit.

scripts/mkinitrd.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+
+compress_level = 19
+
+def write_image(image, files):
+    from pathlib import Path
+    from cdblib import Writer, djb_hash
+    from pyzstd import compress
+
+    with open(image, 'wb') as db:
+        with Writer(db) as writer:
+            for f in files:
+                key = Path(f).name.encode('utf-8')
+                with open(f, 'rb') as input_file:
+                    writer.put(key, compress(input_file.read(), compress_level))
+
+if __name__ == "__main__":
+    from argparse import ArgumentParser
+
+    p = ArgumentParser(description="Generate a jsix initrd image")
+
+    p.add_argument("image", metavar="INITRD", 
+            help="initrd image file to generate")
+
+    p.add_argument("files", metavar="FILE", nargs='+',
+            help="files to add to the image")
+
+    args = p.parse_args()
+    write_image(args.image, args.files)