estuary: break up into multiple crates

This is a mechanical change, which extracts each of the top-level src/
directories into it's own crate. Binaries become crates as well.

As few code changes as possible are made, as needed to get imports
working properly, to fix path issues, and to fix some minor API
version incompatibilities.

Crate cargo versions now use '*' by default, and constrain only when
we have to Cargo.lock already provides pinning to specific versions,
and enables a versioned update workflow. We don't need to *also*
specify dependencies unless they actually matter.

To that end, do specify that we must hold back to tokio 0.2,
because 0.3 isn't supported by hyper & hyperlocal (yet).

.github/workflows/main.yml

@@ -41,9 +41,12 @@ jobs:
       - name: Cache/Restore Rust dependencies.
         uses: actions/cache@v2
         with:
+          # See: https://doc.rust-lang.org/nightly/cargo/guide/cargo-home.html#caching-the-cargo-home-in-ci
+          # TODO: Try https://github.com/Swatinem/rust-cache
           path: |
-            ~/.cargo/registry
-            ~/.cargo/git
+            ~/.cargo/registry/cache
+            ~/.cargo/registry/index
+            ~/.cargo/git/db
             target
           key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
 

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "json/tests/official"]
-	path = json/tests/official
+	path = crates/json/tests/official
 	url = https://github.com/json-schema-org/JSON-Schema-Test-Suite.git