Add bats unit testing to repository

Will recursively look for `*.bats` files and run them with bats-core test suite. Simple sample unit tests for existing scripts are included in `.config/shell/rc.d/test`.

.config/shell/rc.d/test/locale-utf-8.bats

@@ -0,0 +1,15 @@
+setup() {
+  testfile="$BATS_TEST_DIRNAME/../locale-utf-8.sh"
+}
+
+teardown() {
+  export LC_ALL=""
+  export LANG=""
+}
+
+@test "Sets LC_ALL and LANG to en_US.utf-8" {
+  source $testfile
+  expected="en_US.utf-8"
+  [ "$LC_ALL" = "en_US.utf-8" ]
+  [ "$LANG" = "en_US.utf-8" ]
+}