Dharitri transaction snippets

Provides basic functionality for interacting with smart contracts directly from Rust.

It is a base on top of which little interaction programs (or snippets) can be written. Can be used in:

• interactors,
• web servers (in Rust),
• front-end (WebAssembly, via wasm-bindgen/Rust).

It is largely a wrapper around dharitri-sdk and dharitri-sc, combining the two.