Eradication of `data` arg to requests. We no longer need to pass this
value around as we have a) type inference, b) nested object insertion
via `put` and `append`.
Fix `joinPath` numeric type coercion
Detect empty string params and treat them as blank with expectParams()
Fix error logging/stack trace printing.
Update Zmpl - includes debug tokens + error tracing to source template
in debug builds.
Add `jetzig test` command which runs build step `jetzig:test`.
Add `jetzig.testing` namespace which provides test helpers and a test
app.
Add tests to view generator (i.e. include tests for generated routes).
