Release workflow

Describe branches' role & workflows for releases by types.

Branches

master: latest tag
next: next tag
dev: primary branch
Will takeover previous master branch's role.
In order to have control over the timing of releases, added dev branch.
- Triggering a release

All devs will be done on dev.

nightly will merge changes from dev and build nightly dist every day.

RC release: dev → next

dev will be merged into next branch.
Every updates before the latest, should flows from dev to next.

Will publish @next by semantic-release
Patch release: dev → master

dev will be merged into master branch.
latest(stable) release: next → master

next will be merged into master branch.

Will publish @latest by semantic-release