key++: normalize id and lc()

allow signing using an alternate secret key, like in pcpdecrypt()

malloc() new pointers in functions only if not NULL, e.g. pcp_gennonce()

check pub key count in pcp.c before calling verify signature, croak if count==0

Update pod key format spec.

-l show keysig, if any

vault checksum: add keysigs as well

enable formats for secret key exports as well

Add newlines to headers in define.h, so strlen() later catches the whole length.

Z85 headers:
 - currently I use "----- BEGIN ... -----" and "----- END ... -----" as
   header and footer for various z85 encoded outputs. The problem is, that
   the "-" character is part of Z85 chars. An input of 0xc6,0x5a,0x0b,0x13 would
   result z85 encoded as: "-----". So, I cannot be sure, when I find a header
   delimiter, if it's really a delimiter or legitimate z85 encoded content.
   Therefore, another delimiter must be used. "~~~~~ BEGIN .... ~~~~~" seems
   to fit best and "~" is unused in Z85. 
   Then the parser can be enhanced as well. Eg: on startup if a ~ occurs,
   ignore input until the first non-~ appears. Then decode input until a
   ~ or eof appears, ignore everything after. Comments would still be a
   problem though. Currently I ignore lines containing whitespaces. But
   if a file is read blockwise and the blocksize is very small, then a
   comment line may span multiple blocks and isn't recognizable as a
   "line" anymore. Maybe, comments shall start and end with a ~ as well, eg:
   ~ BEGIN KEY ~
   ~ Hash: 987298347 ~
   [z85]
   ~ END KEY ~
   Here I use the same aproach for the headers, since there would also be
   the problem how to recognize them properly if a header crosses boundaries
   or something. By using this scheme, if a ~ is found everything following
   is marked as to be ignored which could be saved as a state when using
   blockmode.

Check is_utf8 license.
  also found in https://gd.meizo.com/_files/lpc/ext/utf8.c

Vault checksum with global vault

Python binding, e.g.:
py % cdll.LoadLibrary("libsodium.so.8")
<CDLL 'libsodium.so.8', handle 800776c00 at 80192a3d0>
py % nacl = CDLL("libsodium.so.8")
py % hash = create_string_buffer('\000' * 64)
py % hash
<ctypes.c_char_Array_65 object at 0x80182c560>
py % hash.raw
'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x...
py % key = create_string_buffer('a' * 32)
py % nacl.crypto_hash_sha256(pointer(hash), pointer(key), 32)
0
py % hash.raw
';\xa3\xf5\xf4;\x92`&\x83\xc1\x9a\xeeb\xa2\x03B\xb0\x84\...
py %