* Added new SafeFile (io.WriteCloser) class + methods to atomically write a file.
* Teach core lib to use SafeFile for all file I/O
* Teach sigtool to use SafeFile for all file I/O
* Cleaned up the public interfaces of sign/ to be more coherent:
- with uniform APIs for marshaling, unmarshaling, serialization.
- removed KeyPair class/interface and stick to PrivateKey as the primary
interface.
* collected common rand utility functions into rand.go
* Teach sigtool to NOT overwrite existing output files (keys, signatures etc.)
* Teach sigtool to use a new --overwrite option for every command that creates
files (generate, sign, encrypt, decrypt)
* encrypt/decrypt will try to use the input file mode/perm where possible
(unless input is stdin).
* Added more tests
- removed spurious check in decrypt() against blocksize
- added additional tests for small sized blocks and inputs smaller than
the blocksize.
- updated README to capture dependencies (protobuf tools)
- aead nonce construction is efficient (replace last 8 bytes of salt
with encoded block# and chunk-size
- increase aead nonce size to 32 bytes
- refactor errors into a separate file
- update "build" to latest version
- updated README.
* Added support to read openssh public keys and encrypted private keys
* reworked private key handling
* made password the default; generating keys without password
requires explicit "--no-password"
