Make it possible to compose application state from multiple indepdenent modules

[pictographer]

We'd like to compose an application from independent modules each of which implements its own routes and has its own state. Tide only supports a single monolithic application state.

To compose an application, it should be sufficient to designate the modules to be composed. Tide-disco should load the corresponding api.toml files, register the appropriate route handler functions, and incorporate the module data in to the web server application state.

The discoverability layer needs access to all the route patterns and documentation, etc. so it can provide discoverable documentation, context-sensitive documentation, and error messages regarding route segment type checking and spelling.

[jbearer]

This was made possible in #21