Bats test

Bats is a bash testing framework. Toml bombadil use it in docker to write realistic test cases without breaking your workstation dotfiles.

Write a new bat test in tests.bat for example :
```
@test "Print version" {
  run bombadil --version
  assert_success
}
```
If you need to add some dotfiles to the docker user home, everything resides in tom_home.
Build the test container docker build -t bombadil-tests ./
Run it docker run -it bombadil-tests :

❯ docker run -it bombadil-tests
 ✓ Print help
 ✓ Print version
 ✓ Symlink bombadil config
 ✓ Links dots

4 tests, 0 failures

Submit a PR to the current release candidate branch.