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/lib/plugins.js

@@ -1,6 +1,7 @@
 const {promisify} = require('util');
 const relative = require('require-relative');
 const pSeries = require('p-series');
+const logger = require('./logger');
 
 module.exports = options => {
   const plugins = {
@@ -10,17 +11,15 @@ module.exports = options => {
   };
   ['verifyConditions', 'verifyRelease'].forEach(plugin => {
     if (!Array.isArray(options[plugin])) {
-      plugins[plugin] = promisify(
-        normalize(
-          options[plugin],
-          plugin === 'verifyConditions' ? '@semantic-release/condition-travis' : './plugin-noop'
-        )
+      plugins[plugin] = normalize(
+        options[plugin],
+        plugin === 'verifyConditions' ? '@semantic-release/condition-travis' : './plugin-noop'
       );
     } else {
       plugins[plugin] = async pluginOptions => {
         return pSeries(
           options[plugin].map(step => {
-            return () => promisify(normalize(step, './plugin-noop'))(pluginOptions);
+            return () => normalize(step, './plugin-noop')(pluginOptions);
           })
         );
       };
@@ -31,13 +30,16 @@ module.exports = options => {
 };
 
 const normalize = (pluginConfig, fallback) => {
-  if (typeof pluginConfig === 'string') return relative(pluginConfig).bind(null, {});
-
-  if (pluginConfig && typeof pluginConfig.path === 'string') {
-    return relative(pluginConfig.path).bind(null, pluginConfig);
+  if (typeof pluginConfig === 'string') {
+    logger.log('Load plugin %s', pluginConfig);
+    return promisify(relative(pluginConfig).bind(null, {}));
   }
 
-  return require(fallback).bind(null, pluginConfig || {});
+  if (pluginConfig && typeof pluginConfig.path === 'string') {
+    logger.log('Load plugin %s', pluginConfig.path);
+    return promisify(relative(pluginConfig.path).bind(null, pluginConfig));
+  }
+  return promisify(require(fallback).bind(null, pluginConfig || {}));
 };
 
 module.exports.normalize = normalize;