* Split the long `try` block into multiple `try/catch` blocks
* Consistently use System.err.println and System.exit on errors
* System.out.println an information message before falling back to `broadcastPayment`
This is a breaking change, but the existing code is not using futures properly and
fixing this is worth the breakage.
* Instead of returning `null`, return a failed future
* Instead of throwing errors, return failed futures
Adds the picocli-codegen annotation processor.
To build the documentation use `gradle bitcoinj-wallettool:asciidoctor`. The results are in:
* wallettool/build/generated-picocli-docs/wallet-tool.adoc (asciidoc source)
* wallettool/build/docs/html5/wallet-tool.html (HTML version)
* wallettool/build/docs/manpage/wallet-tool.1 (man format)
