feat: support multiple branches and distribution channels

- Allow to configure multiple branches to release from
- Allow to define a distribution channel associated with each branch
- Manage the availability on distribution channels based on git merges
- Support regular releases, maintenance releases and pre-releases
- Add the `addChannel` plugin step to make an existing release available on a different distribution channel

BREAKING CHANGE: the `branch` option has been removed in favor of `branches`

The new `branches` option expect either an Array or a single branch definition. To migrate your configuration:
- If you want to publish package from multiple branches, please the configuration documentation
- If you use the default configuration and want to publish only from `master`: nothing to change
- If you use the `branch` configuration and want to publish only from one branch: replace `branch` by `branches` (`"branch": "my-release-branch"` => `"branches": "my-release-branch"`)

lib/definitions/constants.js

@@ -1,7 +1,9 @@
-const RELEASE_TYPE = ['prerelease', 'prepatch', 'patch', 'preminor', 'minor', 'premajor', 'major'];
+const RELEASE_TYPE = ['patch', 'minor', 'major'];
 
 const FIRST_RELEASE = '1.0.0';
 
+const FIRSTPRERELEASE = '1';
+
 const COMMIT_NAME = 'semantic-release-bot';
 
 const COMMIT_EMAIL = 'semantic-release-bot@martynus.net';
@@ -15,6 +17,7 @@ const SECRET_MIN_SIZE = 5;
 module.exports = {
   RELEASE_TYPE,
   FIRST_RELEASE,
+  FIRSTPRERELEASE,
   COMMIT_NAME,
   COMMIT_EMAIL,
   RELEASE_NOTES_SEPARATOR,