v0.2

Added some features:

- unxor now uses standard input and output for more flexibility when
used from command line interfaces. It also has cleaner output

- unxor can xor any standard input or file with an arbitrary key
(useful for tests, or just plain xoring of data)

- New plaintex-attack: this one uses a lot more guesswork so results
may be much less reliable. For a key of length n, every other nth byte
is kept from the cyphertext and the search term, in order to locate a
possible location. Assuming the full search text is present there, the
keystream is deduced.