feat: Refactor CLI to run with one command, improve logs, modularize, add tests

- Run with one command and do not rely on error exit codes to stop the process when a release is not necessary
- Break `index.js` in smaller modules in order to improve testability and simplify the code
- Add several missing unit and integration tests to reach 100% coverage
- Integration tests now test end to end, including publishing to Github (with http://www.mock-server.com on Docker)
- Use `tj/commander.js` to print an help message, verify and parse CLI arguments
- Semantic-release can now be called via Javascript API: `require('semantic-release')(options)`
- Remove npmlog dependency and add more log messages
- Logger is now passed to plugins
- Add debug logs with `visionmedia/debug`. `debug` is enabled for both semantic-release and plugins with `--debug`
- Use `kevva/npm-conf` in place of the deprecated `npm/npmconf`
- Pass lastRelease, nextRelease and commits to generate-notes plugin
- In dry-run mode, print the release note instead of publishing it to Github as draft, and skip the CI verifications
- The dry-run mode does not require npm and Github TOKEN to be set anymore and can be run locally

BREAKING CHANGE: Semantic-Release must now be executed with `semantic-release` instead of `semantic-release pre && npm publish && semantic-release post`.
BREAKING CHANGE: The `semantic-release` command now returns with exit code 0 on expected exception (no release has to be done, running on a PR, gitHead not found, other CI job failed etc...). It only returns with 1 when there is an unexpected error (code error in a plugin, plugin not found, git command cannot be run etc..).
BREAKING CHANGE: Calling the `semantic-release` command with unexpected argument(s) now exit with 1 and print an help message.
BREAKING CHANGE: Semantic-Release does not rely on `npmlog` anymore and the log level cannot be configured. Debug logs can be activated with CLI option `--debug` or with environment variable `DEBUG=semantic-release:*`
BREAKING CHANGE: The CLI options `--debug` doesn't enable the dry-run mode anymore but activate the debugs. The dry run mode is now set with the CLI command `--dry-run` or `-d`.

src/cli.js

@@ -0,0 +1,59 @@
+const program = require('commander');
+const SemanticReleaseError = require('@semantic-release/error');
+const logger = require('./lib/logger');
+
+function list(values) {
+  return values.split(',').map(value => value.trim());
+}
+
+module.exports = async () => {
+  program
+    .name('semantic-release')
+    .description('Run automated package publishing')
+    .option('-b, --branch <branch>', 'Branch to release from')
+    .option('--github-token <token>', 'Token to authenticate with Github API')
+    .option('--github-url <url>', 'GitHub Enterprise endpoint')
+    .option('--github-api-path-prefix <prefix>', 'Prefix of the GitHub Enterprise endpoint')
+    .option(
+      '--verify-conditions <paths>',
+      'Comma separated list of paths or packages name for the verifyConditions plugin',
+      list
+    )
+    .option('--get-last-release <path>', 'Path or package name for the getLastRelease plugin')
+    .option('--analyze-commits <path>', 'Path or package name for the analyzeCommits plugin')
+    .option(
+      '--verify-release <paths>',
+      'Comma separated list of paths or packages name for the verifyRelease plugin',
+      list
+    )
+    .option('--generate-notes <path>', 'Path or package name for the generateNotes plugin')
+    .option('--debug', 'Output debugging information')
+    .option(
+      '-d, --dry-run',
+      'Dry-run mode, skipping verifyConditions, publishing and release, printing next version and release notes'
+    )
+    .parse(process.argv);
+
+  if (program.debug) {
+    // Debug must be enabled before other requires in order to work
+    require('debug').enable('semantic-release:*');
+  }
+
+  try {
+    if (program.args.length > 0) {
+      program.outputHelp();
+      process.exitCode = 1;
+    } else {
+      await require('./index')(program);
+    }
+  } catch (err) {
+    // If error is a SemanticReleaseError then it's an expected exception case (no release to be done, running on a PR etc..) and the cli will return with 0
+    // Otherwise it's an unexpected error (configuration issue, code issue, plugin issue etc...) and the cli will return 1
+    if (err instanceof SemanticReleaseError) {
+      logger.log(`%s ${err.message}`, err.code);
+    } else {
+      process.exitCode = 1;
+      logger.error(err);
+    }
+  }
+};