Create Lorem_Ipsum.txt compressed using mix of checksums

This uses the same 1000 byte blocks as before, with six streams
each of one block. The key difference is each stream uses a
different checksum!

$ cat Lorem_Ipsum.1kb1.txt | xz -C crc64 > p1
$ cat Lorem_Ipsum.1kb2.txt | xz -C crc32 > p2
$ cat Lorem_Ipsum.1kb3.txt | xz -C sha256 > p3
$ cat Lorem_Ipsum.1kb4.txt | xz -C none > p4
$ cat Lorem_Ipsum.1kb5.txt | xz -C crc32 > p5
$ cat Lorem_Ipsum.1kb6.txt | xz -C crc64 > p6
$ cat p1 p2 p3 p4 p5 p6 > Lorem_Ipsum.txt.mixed1k.xz
$ cat Lorem_Ipsum.txt.mixed1k.xz | unxz | diff Lorem_Ipsum.txt -

i.e. The six streams use CRC64, CRC32, SHA256, no checksum, CRC32 and CRC64.
Check bgz.py treats mixed checksums as an error