Is your feature request related to a problem? Please describe.
I would like to use a new Bats feature or behavior (specifically the global variable $BATS_FILE_TMPDIR) and I want to make sure that the version of Bats that's running the test actually has this capability.

Describe the solution you'd like
Add a new global variable (e.g. $BATS_VERSION) that can be used in a test to do whatever is needed. It would hold the release version of the Bats executable that's running the test. With it I could write something like this:

setup() {
    # require 1.6.0 or later
    batsver=( ${BATS_VERSION//./ } )
    if [[ ((${batsver[0]} -eq 1) && (${batsver[1]} -lt 6)) || (${batsver[0]} -lt 1) ]]; then
        skip "Minimum Bats version required: 1.6.0 (running: $BATS_VERSION)"
    fi
}

Describe alternatives you've considered
Alternately, there could be a new assertion that could be run to ensure a minimum version is being used to execute the test, similar to Perl's use 5.008; mechanism, e.g.

@test "Bats version check" {
   assert_version "1.6.0"
}

Adding a new assert function is not to be done lightly, though, and the variable allows more control (skipping if used in setup as I have it, or aborting if used in setup_file with an exit).

Additional context
none