SHA3 xof shake128 and shake256

[immoschuett]

Hi @staticfloat,

i added some implementations of the extended output function shake, since i needed them for my work. I thought this module could take advantage of it.

This is my first pull request, so i'm sorry if anything is not along the usual workflow. Plealse give me feedback!

kind regards.

[staticfloat]

Thanks for your contribution!

These changes seem to have broken the tests, so first resolve that. Next, you'll need to implement a number of tests to ensure that the implementation is correct. Then I can review again.

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (e1af7dd) 99.00% compared to head (241d62b) 98.14%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
- Coverage   99.00%   98.14%   -0.87%     
==========================================
  Files           8        9       +1     
  Lines         402      484      +82     
==========================================
+ Hits          398      475      +77     
- Misses          4        9       +5     

Files	Coverage Δ
src/SHA.jl	100.00% <ø> (ø)
src/shake.jl	93.90% <93.90%> (ø)

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[immoschuett]

Thanks for the fast feedback, i fixed the issues and will add some tests regarding shake soon.

[immoschuett]

Hi @staticfloat

I added some basic testing.
Yet, I did not add any documentation, only comments, but I can work on that later on. I wanted to wait for your first review, because i expect, that some Structs from SHAKE can/should be moved somwhere else.

[staticfloat]

LGTM! Thanks!