With v1.1, move module format to per-endpoint versioning

[ShadowJonathan]

Basically, r0::sync::sync_events -> sync::sync_events::{v3, v4, ...}

This in accordance with Matrix's new Global Versioning, which moves to per-endpoint versioning.

This way, new endpoint versions can easily be added (v4 under the related module, like above) and maintained, instead of having to be in fluid accordance to sub-revisions.

"The matrix version that ruma supports" can then be further granularized, and "old versions" supported much more easily.

It could also open up some form of "specify the matrix versions you want" via crate features, which then define/undefine specific endpoints/versions/features by macros.

More info: https://spec.matrix.org/v1.1/#endpoint-versioning

[jplatte]

Blocked on #792.

[zecakeh]

Isn't this the same as #775?

[jplatte]

Yes, I'll close this as a duplicate.