Add bats_test_suite rule

[fmorency]

The rule can generate bats_test targets for each source file and a test_suite, which encapsulates all tests.

With this rule, one can write a single test suite encapsulating all tests from a source while still being able to run the individual tests.

[fmorency]

@filmil Thank you for merging this PR. Would it be possible to cut a new release with this change?

[filmil]

Happy to. But I wonder why you specifically need a new release?

You should be referring to the repo by commit ID for hermeticity.

[filmil]

To wit, I don't think that bazel-bats really benefits from "releasing" since it's just the source code that gets bundled in the archive anyways. I know we now have the http_archive repo rule in WORKSPACE, but I'm reconsidering it.

[fmorency]

Based on your README, I've been using http_archive in our project. Happy to change if you can provide a new README with updated instructions.

[filmil]

I understand. You can convert your use to git_archive, or you can wait for an update to the README.md.

[filmil]

The instructions in README.md are now fixed. Please try and report back if it doesn't work.