Design and implement an ergonomic surface syntax

[sleexyz]

The current internal representation is not very ergonomic at all. For example:

const endpoint: SafeAPI.Endpoint<{ id: string }, Foo> = new SafeAPI.Snoc({
  previous: new SafeAPI.Snoc({
    previous: new SafeAPI.Nil(),
    middleware: new SafeAPI.Fragment("/getFoo")
  }),
  middleware: new SafeAPI.QueryParams({ id: new StringRep() })
});

Users should have a more ergonomic representation that fulfills the following requirements:

• doesn't incur another level of indentation for each middleware in the stack
• is understandable
• is relatively concise