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`.

test/helpers/mockserver.js

@@ -0,0 +1,89 @@
+import Docker from 'dockerode';
+import getStream from 'get-stream';
+import {mockServerClient} from 'mockserver-client';
+
+const MOCK_SERVER_PORT = 1080;
+const MOCK_SERVER_HOST = 'localhost';
+const docker = new Docker();
+let container;
+
+/**
+ * Download the `mockserver` Docker image, create a new container and start it.
+ *
+ * @return {Promise} Promise that resolves when the container is started.
+ */
+async function start() {
+  await getStream(await docker.pull('jamesdbloom/mockserver:latest'));
+
+  container = await docker.createContainer({
+    Image: 'jamesdbloom/mockserver',
+    PortBindings: {[`${MOCK_SERVER_PORT}/tcp`]: [{HostPort: `${MOCK_SERVER_PORT}`}]},
+  });
+  return container.start();
+}
+
+/**
+ * Stop the `mockserver` Docker container.
+ *
+ * @return {Promise} Promise that resolves when the container is stopped.
+ */
+async function stop() {
+  return container.stop();
+}
+
+/**
+ * @type {Object} A `mockserver` client configured to connect to the current instance.
+ */
+const client = mockServerClient(MOCK_SERVER_HOST, MOCK_SERVER_PORT);
+/**
+ * @type {string} the url of the `mockserver` instance
+ */
+const url = `http://${MOCK_SERVER_HOST}:${MOCK_SERVER_PORT}`;
+
+/**
+ * Set up the `mockserver` instance response for a specific request.
+ *
+ * @param {string} path URI for which to respond.
+ * @param {Object} request Request expectation. The http request made on `path` has to match those criteria in order to be valid.
+ * @param {Object} request.body The JSON body the expected request must match.
+ * @param {Object} request.headers The headers the expected request must match.
+ * @param {Object} response The http response to return when receiving a request on `path`. 
+ * @param {String} [response.method='POST'] The http method for which to respond.
+ * @param {number} [response.statusCode=200] The status code to respond.
+ * @param {Object} response.body The JSON object to respond in the response body.
+ * @return {Object} An object representation the expectation. Pass to the `verify` function to validate the `mockserver` has been called with a `request` matching the expectations.
+ */
+function mock(
+  path,
+  {body: requestBody, headers: requestHeaders},
+  {method = 'POST', statusCode = 200, body: responseBody}
+) {
+  client.mockAnyResponse({
+    httpRequest: {path},
+    httpResponse: {
+      statusCode,
+      headers: [{name: 'Content-Type', values: ['application/json; charset=utf-8']}],
+      body: JSON.stringify(responseBody),
+    },
+    times: {remainingTimes: 1, unlimited: false},
+  });
+
+  return {
+    method,
+    path,
+    headers: requestHeaders,
+    body: {type: 'JSON', json: JSON.stringify(requestBody), matchType: 'ONLY_MATCHING_FIELDS'},
+  };
+}
+
+/**
+ * Verify the `mockserver` has been called with a requestion matching expectations. The `expectation` is created with the `mock` function.
+ *
+ * @param {Object} expectation The expectation created with `mock` function.
+ * @return {Promise} A Promise that resolves if the expectation is met or reject otherwise.
+ */
+async function verify(expectation) {
+  return client.verify(expectation);
+}
+
+export default {start, stop, mock, verify, url};