Add T.Skip(count int, description string)

The spec [1] suggests "ok 23 # SKIP ...", but if you attempt this with:

  t.Pass("# SKIP foo")

you get an extra hyphen ("ok 23 - # SKIP foo") which is parsed as a
successful test (and not a skipped test).

Michael gives the following example to motivate 'count' [2]:

  if ConditionIsMet() {
    t.Ok(Foo(), "foo")
    t.Ok(Bar(), "bar")
  } else {
    t.Skip(2, "condition not met")
  }

The spec example of this is in [3], showing no special syntax for
skipping multiple tests (although there is a special syntax for
skipping *all* the tests).

Also alphabetize TESTS in the Makefile.

[1]: http://testanything.org/tap-version-13-specification.html#skipping-tests
[2]: mndrix/tap-go#6 (comment)
[3]: http://testanything.org/tap-version-13-specification.html#skipping-a-few

Author: wking

util/tap.go

@@ -117,6 +117,14 @@ func escapeNewlines(s string) string {
 	return strings.Replace(strings.TrimRight(s, "\n"), "\n", "\n# ", -1)
 }
 
+// Skip indicates that a test has been skipped.
+func (t *T) Skip(count int, description string) {
+	for i := 0; i < count; i++ {
+		t.printf("ok %d # SKIP %s\n", t.nextTestNumber, description)
+		t.nextTestNumber++
+	}
+}
+
 // Diagnostic generates a diagnostic from the message,
 // which may span multiple lines.
 func (t *T) Diagnostic(message string) {