scripts: Reworked dbgtag.py, added -i/--input, included hex in output

This just gives dbgtag.py a few more bells and whistles that may be
useful:

- Can now parse multiple tags from hex:

    $ ./scripts/dbgtag.py -x 71 01 01 01 12 02 02 02
    71 01 01 01    altrgt 0x101 w1 -1
    12 02 02 02    shrubdir w2 2

  Note this _does_ skip attached data, which risks some confusion but
  not skipping attached data will probably end up printing a bunch of
  garbage for most use cases:

    $ ./scripts/dbgtag.py -x 01 01 01 04 02 02 02 02 03 03 03 03
    01 01 01 04    gdelta 0x01 w1 4
    03 03 03 03    struct 0x03 w3 3

- Included hex in output. This is helpful for learning about the tag
  encoding and also helps identify tags when parsing multiple tags.

  I considered also included offsets, which might help with
  understanding attached data, but decided it would be too noisy. At
  some point you should probably jump to dbgrbyd.py anyways...

- Added -i/--input to read tags from a file. This is roughly the same as
  -x/--hex, but allows piping from other scripts:

    $ ./scripts/dbgcat.py disk -b4096 0 -n4,8 | ./scripts/dbgtag.py -i-
    80 03 00 08    magic 8

  Note this reads the entire file in before processing. We'd need to fit
  everything into RAM anyways to figure out padding.

scripts/parity.py

@@ -46,14 +46,18 @@ def parity(x):
     return popc(x) & 1
 
 
-def main(paths, **args):
+def main(paths, *,
+        hex=False,
+        string=False):
+    hex_ = hex; del hex
+
     # interpret as sequence of hex bytes
-    if args.get('hex'):
+    if hex_:
         bytes_ = [b for path in paths for b in path.split()]
         print('%01x' % parity(crc32c(bytes(int(b, 16) for b in bytes_))))
 
     # interpret as strings
-    elif args.get('string'):
+    elif string:
         for path in paths:
             print('%01x  %s' % (parity(crc32c(path.encode('utf8'))), path))