Automate Release Documentation

[OR13]

We need a top level script and documentation for how mono repo releases should work.

• how to checkout, build, publish and commit a new version
• how a standard root level change log is built for each new version of element.
• how commit hooks are used to produce this change log
• how documentation is generated hosted (for now only 1 version of documentation should be hosted, in the future we will need to preserve older versions).

element-core has a lot of this defined already, we need to pull some of that up a level, and test some releases to see that things are running smoothly.

[OR13]

@gjgd do you think this is done? maybe you can publish some npm releases and see how it feels?