release v1.13.1

release v1.13.0

robustio: copy from cmd/go/internal/robustio (#239)

Copied from Go commit b18b05881691861c4279a50010829150f1684fa9.

README: add context on maintainers and a testscript overview with lin…

…ks (#225)

Help give some context for people who might be evaluating using this repo and are wondering:

* what is the bus factor for the repo?
* who are the maintainers?
* are the maintainer(s) of this repo still interested in this repo (including, are they still using it)?
* are other people using testscript?
* where did testscript come from?

Obviously, someone can hunt around to determine many of these things on their own,
but the intent is to help make that process more efficient.

Updates #196.

release v1.10.0

testscript: update docs on set variables

We have been setting `/`, `:`, and `$` for some time,
but they weren't documented. Do that.

`goversion` doesn't belong here, as it was moved to `gotooltest`.

`TMPDIR` was slightly wrong; it has started with a period for some time,
to ensure that tools like `go list ./...` don't descend into it.

imports: Update goosList and goarchList

Revert "gotooltest: proxy the new GOMODCACHE env var too" (#136)

We started making gotooltest share the host's module download cache with
test scripts, since we did it with GOCACHE and it initially made sense.

However, the upside is significantly smaller for GOMODCACHE compared to
GOCACHE. The build cache can save a significant amount of time, since
many tools have to load or build Go packages as part of their tests.
In contrast, few tests download modules, and those which do tend to
download those modules from a local proxy like goproxytest, which is
very fast already.

The downsides of sharing the module download cache are a few:

* We don't share GOPATH, and since the default GOMODCACHE is
  GOPATH/pkg/mod, sharing one and not the other is unexpected and
  inconsistent.

* Upstream testscript shares GOCACHE, but does not share GOMODCACHE.
  See golang/go#42017.

* Losing a degree of isolation in the tests is a downside in itself,
  especially given that sharing GOMODCACHE isn't crucial.

This reverts commit c5fd45a.

Note that we keep the env.txt test in place, just flipping the
expectation that GOMODCACHE does not contain ${WORK}.

ci: include upcoming go1.16 in build matrix (#124)

testscript: support Go 1.16, move to Actions

https://go-review.googlesource.com/c/go/ /250977 adds a new method to
the testing.testDeps interface, so mirror that here in our no-op
implementation too.

While at it, replace Travis with GitHub Actions, which is faster and
easier to use. We still test on Linux, Mac, and Windows, and with the
two latest Go versions. Otherwise, the config is a straight port, and we
run the same commands.