Fix issue #22, Private key and seed can be sent to the node

[ghost]

See issue #22.
Note: I've never used typescript before. It works, but may need some changes.

[rawrmaan]

Love this idea--just need to add buffer to the package.json in order support non-node.js environments. I'll try to get to testing this soon.

[rawrmaan]

Since v11/v12 are now out, this PR can no longer be merged unless it is updated to support creating state blocks.

[roccomuso]

this module make no sense without this PR merged, that address a major security concern.