Sync to linguist 7.2.0: heuristics.yml support (#189)

Sync \w Github Linguist v7.2.0

Includes new way of handling `heuristics.yml` and
all `./data/*` re-generated using Github Linguist [v7.2.0](https://github.com/github/linguist/releases/tag/v7.2.0)
release tag.

 - many new languages
 - better vendoring detection
 - update doc on update&known issues.

data/rule/rule_test.go

@@ -0,0 +1,39 @@
+package rule
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const lang = "ActionScript"
+
+var fixtures = []struct {
+	name     string
+	rule     Heuristic
+	numLangs int
+	matching string
+	noMatch  string
+}{
+	{"Always", Always(MatchingLanguages(lang)), 1, "a", ""},
+	{"Not", Not(MatchingLanguages(lang), regexp.MustCompile(`a`)), 1, "b", "a"},
+	{"And", And(MatchingLanguages(lang), regexp.MustCompile(`a`), regexp.MustCompile(`b`)), 1, "ab", "a"},
+	{"Or", Or(MatchingLanguages(lang), regexp.MustCompile(`a|b`)), 1, "ab", "c"},
+}
+
+func TestRules(t *testing.T) {
+	for _, f := range fixtures {
+		t.Run(f.name, func(t *testing.T) {
+			assert.NotNil(t, f.rule)
+			assert.NotNil(t, f.rule.Languages())
+			assert.Equal(t, f.numLangs, len(f.rule.Languages()))
+			assert.Truef(t, f.rule.Match([]byte(f.matching)),
+				"'%s' is expected to .Match() by rule %s%v", f.matching, f.name, f.rule)
+			if f.noMatch != "" {
+				assert.Falsef(t, f.rule.Match([]byte(f.noMatch)),
+					"'%s' is expected NOT to .Match() by rule %s%v", f.noMatch, f.name, f.rule)
+			}
+		})
+	}
+}