Add CI fixes and improvements (#780)

* Update GolangCI-lint and lint config

The `algo` parameter for the `unparam` linter has been removed and we
should thus no longer specify it. Also, bumping the GolangCI-lint
version to the latest available minor release.

See: mvdan/unparam@e6a6d1c51b

* Fix and improve bintray CI script

* Further CI setup improvements

* Split-out CI steps into stand-alone scripts

ci/test.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+set -u -e -x -o pipefail
+
+if [[ -n "${REPORT_COVERAGE+cover}" ]]; then
+  # Retrieve and prepare CodeClimate's test coverage reporter.
+  curl -L https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > ./cc-test-reporter
+  chmod +x ./cc-test-reporter
+  ./cc-test-reporter before-build
+fi
+
+# Run all the tests with the race detector and generate coverage.
+go test -v -race -coverprofile c.out ./...
+
+if [[ -n "${REPORT_COVERAGE+cover}" && "${TRAVIS_SECURE_ENV_VARS}" == "true" ]]; then
+  # Upload test coverage to CodeClimate.
+  ./cc-test-reporter after-build
+fi