Release 3.0

1. Switch from using SHA1 checksums in the bmap file to SHA256. This required
   bmap format change. The new format version is 1.4. BmapCopy (and thus,
   bmaptool supports all the older versions too). Now it is possible to use any
   hash functions for checksumming, not only SHA256, but SHA256 is the default
   for BmapCreate.

2. Support OpenPGP (AKA gpg) signatures for the bmap file. From now on the bmap
   file can be signed with gpg, in which case bmaptool verifies the bmap file
   signature. If the signature is bad, bmaptool exits with an error message.
   The verification can be disabled with the --no-sig-verify option.

   Both detached and "in-band" clearsign signatures are supported. Bmaptool
   automatically discovers detached signatures by checking ".sig" and ".asc"
   files.

3. The Fiemap module (and thus, bmaptool) now always synchronizes the image
   before scanning it for mapped areas. This is done by using the
   "FIEMAP_FLAG_SYNC" flag of the FIEMAP ioctl.

   The reason for synchronizing the file is bugs in early implementations of
   FIEMAP in the kernel and file-systems, and synchronizing the image is a
   known way to work around the bugs.