Add encryption support for OOXML

[stephane-rouleau]

This is a port of the C++ library https://github.com/herumi/msoffice to add native Python support for encryption.

OLE file writing had to be ported over as olefile does not do the heavy lifting at this stage.

I have a few more tests I'd like to run, especially with larger files, but I wanted to get your feedback on this initial stab at it.

[nolze]

So amazing! This is monumental work.
Basically everything seems fine, but let me take some time to review it.
I hope to merge this with minimal changes, and do more careful preparation for a new release afterwards.

[codecov]

Codecov Report

Attention: 34 lines in your changes are missing coverage. Please review.

Comparison is base (57cae1c) 92.00% compared to head (5cd2ee1) 92.24%.
Report is 4 commits behind head on master.

Files	Patch %	Lines
msoffcrypto/method/container/ecma376_encrypted.py	91.78%	28 Missing ⚠️
msoffcrypto/method/ecma376_agile.py	97.10%	4 Missing ⚠️
msoffcrypto/format/ooxml.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #86      +/-   ##
==========================================
+ Coverage   92.00%   92.24%   +0.23%     
==========================================
  Files          14       15       +1     
  Lines        1364     1843     +479     
==========================================
+ Hits         1255     1700     +445     
- Misses        109      143      +34     

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[nolze]

I made and commited some small edits, including:

• Update LICENSE.txt to include the text for herumi/msoffice (BSD-3)
• Run formatter (black)
• Change some function names to the snake case from the camel case
• Edit comments
• Edit README

Diff: https://github.com/stephane-rouleau/msoffcrypto-tool/compare/03ea21f...5cd2ee1?diff=split&w=

Any feedback would be appreciated. I will merge this if there seems no problem.

[stephane-rouleau]

Thank you so much for this, I will review soon and let you know!

[stephane-rouleau]

It looks good to me, thank you for the cleanup!

[nolze]

Merged, thanks a lot!