Release 1.0.0, write versioning policy

[RangerMauve]

We need to signal breaking changes to users when they update their instances.

Specifically these changes:

• Breaking changes to the HTTP API (changed field schemas, removed fields)
• Breaking changes in storage (data that will no longer be available, any manual migration)
• Breaking chances in sync with clients (if clients need to update their versions to be able to sync with the server)

Ideally we should release 1.0.0 ASAP so we can rely on regular semantic versioning since we're at 0.x.x right now.

[RangerMauve]

Adding this to discuss in sprint 17

[RangerMauve]

Let's punt this to when we restart on comapeo-sass