Add Themis in crypto section

[popaaaandrei]

https://github.com/cossacklabs/themis - high-level cryptographic services library for mobile and server platforms

[twof]

It doesn't look like the library has a Package.swift

[popaaaandrei]

It's a starting point as the library is multi-platform. Swift and Objective-C are using wrappers for the C library. I am using it in a Vapor project for ECC encryption and works perfectly.

https://github.com/cossacklabs/SwiftThemis
https://github.com/cossacklabs/SwiftCThemis