Finish up gitignore implementation

tools/ignorefiles/api.go

@@ -0,0 +1,25 @@
+package ignorefiles
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+)
+
+var _ = fmt.Print
+
+type IgnoreFile interface {
+	LoadString(string) error
+	LoadBytes([]byte) error
+	LoadLines(...string) error
+	LoadFile(io.Reader) error
+	LoadPath(string) error
+
+	// relpath is the path relative to the directory containing the ignorefile.
+	// When is_ignored is true, linenum_of_matching_rule will be the line
+	// number of the rule causing relpath to be ignored and pattern is the
+	// textual representation of the matching pattern.
+	IsIgnored(relpath string, ftype fs.FileMode) (is_ignored bool, linenum_of_matching_rule int, pattern string)
+}
+
+func NewGitignore() IgnoreFile { return &Gitignore{index_of_last_negated_rule: -1} }