BIP-374: add generated test vector .csv files

[theStack]

Even though the test vector generation script is available for BIP-374, I think it's generally a good practice to store the generated test vectors available in the BIP repository as well, so that everyone can verify that it yields deterministic results. In case refactoring / bugfix changes are needed in the test generation script in the future (e.g. #1729 for a recent example), one can check that the results are still equal.

Can be tested by:

$ cd ./bip-0374
$ sha256sum *.csv
$ ./gen_test_vectors.py
$ sha256sum *.csv

Both sha256sum commands should result in the same hash values.

[murchandamus]

cc @andrewtoth

[andrewtoth]

ACK a00064f

[jonatack]

Concept and tested ACK a00064f