Add standard interface for file diff functions

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.h

@@ -20,6 +20,7 @@
 
 typedef void (*configfn)(const char *name, const char *value);
 typedef void (*filepair_fn)(struct diff_filepair *pair);
+typedef void (*linediff_fn)(char *line, int len);
 
 struct cacheitem {
 	char *name;
@@ -117,9 +118,15 @@ extern int chk_positive(int result, char *msg);
 extern int hextoint(char c);
 
 extern void *cgit_free_commitinfo(struct commitinfo *info);
+
+extern int cgit_diff_files(const unsigned char *old_sha1,
+			   const unsigned char *new_sha1,
+			   linediff_fn fn);
+
 extern void cgit_diff_tree(const unsigned char *old_sha1,
 			   const unsigned char *new_sha1,
 			   filepair_fn fn);
+
 extern void cgit_diff_commit(struct commit *commit, filepair_fn fn);
 
 extern char *fmt(const char *format,...);