Implement an accept function accepts if next character doesn't match some provided character

This makes it easy to do something like "accept until".

src/hb/proc.h

@@ -59,6 +59,7 @@ typedef bool hb_proc_pred(hb_rune);
 hb_rune hb_proc_accept(hb_proc* proc);
 void hb_proc_accept_count(hb_proc* proc, size_t count);
 bool hb_proc_accept_if(hb_proc* proc, hb_rune c);
+bool hb_proc_accept_if_not(hb_proc* proc, hb_rune c);
 size_t hb_proc_accept_if_matches(hb_proc* proc, char const* match);
 size_t hb_proc_accept_if_matches_line_terminator(hb_proc* proc);
 bool hb_proc_accept_if_predicate(hb_proc* proc, hb_proc_pred* pred);

src/hb/proc/accept.c

@@ -63,6 +63,28 @@ bool hb_proc_accept_if(hb_proc* proc, hb_rune c) {
     return true;
 }
 
+/**
+ * Accept the following character if it is not `c`.
+ * Won't match or cause an error if there are no characters remaining.
+ * Undefined behaviour if `c == HB_EOF`.
+ *
+ * @param proc proc
+ * @param c character to not match
+ * @return false if nothing was accepted, true otherwise
+ */
+bool hb_proc_accept_if_not(hb_proc* proc, hb_rune c) {
+    hb_eof_rune n = hb_proc_peek_eof(proc);
+
+    // n == c takes care of n != HB_EOF
+    if (n == c) {
+        return false;
+    }
+
+    hb_proc_accept(proc);
+
+    return true;
+}
+
 /**
  * Accept the following characters if they match `match`.
  * Won't match or cause an error if there are not enough characters remaining.