Added Toml types from SEP1

[tobinbc]

https://github.com/stellar/js-stellar-sdk/issues/371

Added all the fields I could find in SEP1; and other sources when building my Anchor.

They are not readonly because if going in the other direction it can be desired to assemble the object first before it is tomlified.

Is there any desire to bring in the reverse? e.g.

const TOML = require("@iarna/toml");
const body = TOML.stringify(config);