Provide native implementations of supported algorithms

[jvz]

After working out some proof of concept code to try out https://github.com/mit-plv/fiat-crypto for elliptic curve stuff, it turns out to be fairly straightforward to build and include native variants of the algorithms being provided in the Java API through some fairly minimal JNI boilerplate. Since every crypto algorithm tends to have a reference C implementation, most of the symmetric algorithms can be easily imported that way rather than having to be ported again (the Java implementations are ported from C in the first place).

While the plain reference implementations are likely similar in performance to the Java ones, there are several assembly optimizations available for these algorithms and can be included for supported platforms (mostly for x86-64, though some may have additional platforms optimized).

[jvz]

Still needs chacha-opt and poly1305-opt integrated into the build for assembler-optimized variants.