Also, update TravisCI goclean script to remove the special casing which
ignored 'Id' from the lint output since that exception is no longer
needed. It was previously required due to the old version of btcjson,
but that is no longer in the repo.
This commit causes TravisCI to run several tools on each pull request and
commit to help ensure the code quality remains high. This includes gofmt,
goimports, golint, go vet, the race detector, and coverage stats.
Also, it instructs TravisCI to use nicer container-based builds.
