Support "Cryptography API: Next Generation" on Windows

[paperchalice]

Use Cryptography API: Next Generation, because UWP doesn't support old api.
There is a simpler implementation if we don't care about RSA:

BCryptGenRandom(NULL, (PUCHAR)p, (ULONG)n, BCRYPT_USE_SYSTEM_PREFERRED_RNG);

[sjaeckel]

Thanks for the PR :)

Could you please check how we did the bcrypt integration in ltc and copy that instead?

https://github.com/libtom/libtomcrypt/blob/develop/src/prngs/rng_get_bytes.c

[sjaeckel]

Changes look fine!

Can you please squash the two commits and then we're ready to merge.

Thanks again :)

[levitte]

Yup, looks good to me too