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/get-version-head.js

@@ -1,5 +1,7 @@
-const SemanticReleaseError = require('@semantic-release/error');
 const execa = require('execa');
+const debug = require('debug')('semantic-release:get-version-head');
+const SemanticReleaseError = require('@semantic-release/error');
+const {debugShell} = require('./debug');
 
 /**
  * Get the commit sha for a given tag.
@@ -10,8 +12,11 @@ const execa = require('execa');
  */
 async function gitTagHead(tagName) {
   try {
-    return (await execa('git', ['rev-list', '-1', '--tags', tagName])).stdout;
+    const shell = await execa('git', ['rev-list', '-1', '--tags', tagName]);
+    debugShell('Get git tag head', shell, debug);
+    return shell.stdout;
   } catch (err) {
+    debug(err);
     return null;
   }
 }
@@ -24,7 +29,9 @@ async function gitTagHead(tagName) {
  * @return {boolean} `true` if the commit `sha` is in the history of the current branch, `false` otherwise.
  */
 async function isCommitInHistory(sha) {
-  return (await execa('git', ['merge-base', '--is-ancestor', sha, 'HEAD'], {reject: false})).code === 0;
+  const shell = await execa('git', ['merge-base', '--is-ancestor', sha, 'HEAD'], {reject: false});
+  debugShell('Check if commit is in history', shell, debug);
+  return shell.code === 0;
 }
 
 /**
@@ -41,14 +48,17 @@ async function isCommitInHistory(sha) {
 module.exports = async (gitHead, version) => {
   // Check if gitHead is defined and exists in release branch
   if (gitHead && (await isCommitInHistory(gitHead))) {
+    debug('Use gitHead: %s', gitHead);
     return gitHead;
   }
 
   // Ushallow the repository
-  await execa('git', ['fetch', '--unshallow', '--tags'], {reject: false});
+  const shell = await execa('git', ['fetch', '--unshallow', '--tags'], {reject: false});
+  debugShell('Unshallow repo', shell, debug);
 
   // Check if gitHead is defined and exists in release branch again
   if (gitHead && (await isCommitInHistory(gitHead))) {
+    debug('Use gitHead: %s', gitHead);
     return gitHead;
   }
 
@@ -59,6 +69,7 @@ module.exports = async (gitHead, version) => {
 
     // Check if tagHead is found and exists in release branch again
     if (tagHead && (await isCommitInHistory(tagHead))) {
+      debug('Use tagHead: %s', tagHead);
       return tagHead;
     }
   }