Declare support for Matrix 1.5

Complete changelog v1.5

Client-Server API

Backwards Compatible Changes

• Add m.reference relations, as per MSC3267.
  • Only missing aggregation, if anything?

Spec Clarifications (NOTE: non-actionable things removed, as well as things we don't have implemented at all yet, e.g. refresh tokens clarification would be fixed when implementing refresh tokens)

• Define a 400 response from /_matrix/client/v3/directory/rooms/{roomAlias}. (#1286)
  • We already return 400, but not the correct errcode

Application Service API

Spec Clarifications

• Clarify that application services can only register an interest in local users, as per MSC3905. (#1305)
  • From the looks of it, we just compile the provided regex, but don't check if the user is local