bsdiff4: binary diff and patch using the BSDIFF4-format

The code is mostly derived from cx_bsdiff (written by Anthony Tuininga, http://cx-bsdiff.sourceforge.net/). The cx_bsdiff code in turn was derived from bsdiff, the standalone utility produced for BSD which can be found at http://www.daemonology.net/bsdiff. In addition to the two functions (diff and patch) cx_bsdiff provides, this package includes:

an interface to the BSDIFF4-format
command line interfaces: bsdiff4 and bspatch4
tests

The bsdiff4 package defines the following high level functions:

diff(src_bytes, dst_bytes) -> bytes: Return a BSDIFF4-format patch (from src_bytes to dst_bytes) as bytes.
patch(src_bytes, patch_bytes) -> bytes: Apply the BSDIFF4-format patch_bytes to src_bytes and return the bytes.
file_diff(src_path, dst_path, patch_path): Write a BSDIFF4-format patch (from the file src_path to the file dst_path) to the file patch_path.
file_patch(src_path, dst_path, patch_path): Apply the BSDIFF4-format file patch_path to the file src_path and write the result to the file dst_path.
file_patch_inplace(path, patch_path): Apply the BSDIFF4-format file patch_path to the file path in place.

Example:

>>> import bsdiff4
>>> a = 100000 * b'a'
>>> b = bytearray(a)
>>> b[100:106] = b' diff '
>>> p = bsdiff4.diff(a, bytes(b))
>>> len(p)
154
>>> bsdiff4.patch(a, p) == b
True