Tomb/extras/kdf

BUILD
------

Just type make.
You need a recent development version of libgcrypt installed.
On Debian 7 (not earlier) the libgcrypt11-dev package works:
 # apt-get install libgcrypt11-dev

PLANS
------

While this can be useful for general purpose, it specially fits tomb, and it's designed for easy integration and compilation.

Binary name will then be:
tomb-kdf-${algo}
tomb-kdf-${algo}-gensalt
tomb-kdf-${algo}-getiter

hexencode (or similar utils, should they be developed), go with:
tomb-utils-hexencode

Base64 vs hexencode
-------------------

While base64 is easier to use (shell command, more compact), pbkdf2 use hex
in its specifications.
This could be solved with an option (-x for hex, defaults to base64)