Add test.sh. (#173)

This emulates the test matrix that gets run in CI, making it easier to
find failures locally.

There was one conflict in the matrix: when JSON is enabled and TLS is
disabled, two of the doctests would fail. This was previous worked
around as an exclude in the github workflow. I changed the JSON doctest
to use HTTP instead.

.github/workflows/test.yml

@@ -37,9 +37,6 @@ jobs:
         what:
           - "--doc"
           - "--tests"
-        exclude:
-          - tls: ""
-            what: "--doc"
     env:
       RUST_BACKTRACE: "1"
       RUSTFLAGS: "-D dead_code -D unused-variables -D unused"