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).
Runs a development server and auto-reloads when changes are detected to
files.
Note that a "change" is just an mtime update, Zig does a more
intelligent change detection so avoids unnecessary recompiles, so the
server reloads very quickly.
Remove old bash script for setting up a new project, do everything in
Zig to make it platform agnostic and give us an easy place to add
scaffolding commands in future.
