chore: add standard-version and release script

This commit adds the `standard-version` module for managing releases.
When running `npm run release` the following steps are taken.

1. Retreive the current version of your repository by looking at package.json.
2. Bump the version in package.json based on the commits.
3. Prepends to the CHANGELOG based on the commits (uses conventional-changelog under the hood).
4. Create a new commit including the package.json and updated CHANGELOG.
5. Create a new tag with the new version number.

This works best if all commits follow the Conventional Commits specification.
https://www.conventionalcommits.org/en/v1.0.0/

Fixes: #56

Signed-off-by: Lance Ball <lball@redhat.com>

Author: lance

Diff for: CHANGELOG.md

@@ -14,6 +14,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 - Removed support for Node.js 6, 7 and 8 - all of which are EOL at this point. Travis CI modified to test on Node.js 10 and 12.
 
+### Added
+
+- Added support for standard-version and conventional-changelog
+
 ## [1.0.0]
 
 ### Added

Diff for: CONTRIBUTING.md

@@ -14,15 +14,35 @@ ahead of `master`.
 
 ## Changelog
 
-Always update the [CHANGELOG.md](./CHANGELOG.md), following
-[this semantics](https://keepachangelog.com/en/1.0.0/).
+The [CHANGELOG.md](./CHANGELOG.md) will be updated with your commits if you format
+your commit messages following the
+[Conventional Commits specification](https://www.conventionalcommits.org/en/v1.0.0/#summary).
+If you are unsure what prefix to use for a commit, you can consult the
+[package.json](https://github.com/cloudevents/sdk-javascript/blob/master/package.json) file
+in this repository. In the `standard-version.types` section, you can see all of the commit
+types that will be committed to the changelog based on the prefix in the first line of
+your commit message. For example, the commit message:
+
+```log
+fix: removed a bug that was causing the rotation of the earth to change
+```
+
+will show up in the "Bug Fixes" section of the changelog for a given release.
 
 ## Pull Requests
 
 Guidelines about how to perform pull requests.
 
 - before submit the PR, open an issue and link them
 
+### Commit Messages
+
+Please follow the Conventional Commits specification noted above. the first line of
+your commit should be prefixed with a type, be a single sentence with no period, and
+succinctly indicate what this commit changes.
+
+All commit message lines should be kept to fewer than 80 characters if possible.
+
 ### PR to `develop`
 
 - fixes in the documentation (readme, contributors)