Paasio combined commit for close(start) and other changes:

* Simplify `close(start)` per line note https://github.com/exercism/xgo/commit/a252a4d0908dbcb443c2e9a1e5d8b61b5410bd59#paasio-paasio_test-go-P113
* Drop error return on constructors per nitpicking discussion.
* Add TestVersion per discussion on https://github.com/exercism/exercism.io/issues/1657
* Simplify example a bit, including commenting out untested code.