Large refactor that more closely aligns the codebase to the kj async
style, more clearly exposes an interface for functional testing and
removes cruft. There is a slight increase in coupling between the
Laminar and Http/Rpc classes, but this was always an issue, just until
now more obscured by the arbitrary pure virtual LaminarInterface class
(which has been removed in this change) and the previous lumping
together of all the async stuff in the Server class (which is now
more spread around the code according to function).
This change replaces the use of Websockets with Server Side Events
(SSE). They are simpler and more suitable for the publish-style messages
used by Laminar, and typically require less configuration of the
reverse proxy HTTP server.
Use of gmock is also removed, which eases testing in certain envs.
Resolves#90.
