Initial addition of chacha20 stream cipher module under vlib/x/crypto namespace

[blackshirt]

This pull request add ChaCha20 symetric stream cipher encryption under the new vlib/x/crypto namespace. Its acts as places for supplemetary (or experimental) crypto-related library, like Go did.
This implementation mostly based on RFC 8439 and trying to get as close as possible to the inspiring Go version of chacha20 library.

For this initial PR, it's support two's mode of nonce size, standard size of IETF RFC 8439, ie 12 bytes, and extended nonce size, ie, 24 bytes, based on XChaCha20

Please give a review, thought or feedback. All are welcome.
Thanks

[blackshirt]

@spytheman thanks for reviewing it

[JalonSolov]

Since most of the functions properly check array bounds already, you may want to try some benchmarks to see if adding the @[direct_array_access] attribute will improve the speed (not that it's exactly slow, now, but faster is always better if it still gets the correct answers 😄).

[spytheman]

@blackshirt to fix ./vlib/x/crypto/chacha20/README.md:11:1: error: example is not formatted, run VAUTOFIX=1 ./v check-md -hide-warning vlib/x/crypto/chacha20/README.md 2 times, and commit the result.

[blackshirt]

Since most of the functions properly check array bounds already, you may want to try some benchmarks to see if adding the @[direct_array_access] attribute will improve the speed (not that it's exactly slow, now, but faster is always better if it still gets the correct answers 😄).

I would try writes some preliminary Benchmark in next PR..btw, its in my plan..thanks for suggestion)

[blackshirt]

@blackshirt to fix ./vlib/x/crypto/chacha20/README.md:11:1: error: example is not formatted, run VAUTOFIX=1 ./v check-md -hide-warning vlib/x/crypto/chacha20/README.md 2 times, and commit the result.

Thanks, its done in latest changes

[spytheman]

Excellent work.

[blackshirt]

Excellent work.

Thanks ..with help from great people and awesome vlang communities...
Btw, thanks for all the fixs.