md6-wasm example

Known-good example outputs:

md6(512,"test") = 'd96ce883f4632f826b3bb553fe5cbff8fb00b32b3534b39aa0c0899d1199a8cf28d77e49f2465517dfb12c0f3268b90f8a13d94e6730a74ed2e8312242a9e937'

md6(256,'test') = '93c8a7d0ff132f325138a82b2baa98c12a7c9ac982feb6c5b310a1ca713615bd'

md6(128,'test') = 'a133b0efa199156be653427c6ab85d3d'