Use utf8::reencode_string from git

This replaces the iconv-support in cgit with similar functions already
existing in git.

Signed-off-by: Lars Hjemli <hjemli@gmai.com>
diff --git a/cgit.h b/cgit.h
index 6c7a941..6291c58 100644
--- a/cgit.h
+++ b/cgit.h
@@ -16,6 +16,7 @@
 #include <log-tree.h>
 #include <archive.h>
 #include <xdiff/xdiff.h>
+#include <utf8.h>
 
 
 /*