Add Modver to CI. Update badges. (#4)

go mod tidy

Version v2.1.0 added by Taggo

Upgrade dependencies.

Update x/crypto dependency to address advisory https://deps.dev/advis…

…ory/OSV/GO-2020-0012.

Add coveralls.io coverage and badge.

Add a Wikipedia link to the Readme. Capitalize Merkle in documentation.

Add Readme and GitHub test workflow.

Simplify the code, and make it about 20% faster, by removing unneeded…

… concurrency.

Version 2: Proof.Hash is now smart enough not to need the caller to L…

…eafHash its arg first.