Skip generating ignores for certain ligatures.

- Logic ripped from FiraCode, not currently applicable to Fantasque
 Sans

 - Some potential ligatures ( <*>, <$> ), can be arbitrarily extended
 while still making sense: ( <<<$>>>, etc). Standard 'ignore' rules will
 prevent this from displaying, so we can skip those for certain
 ligatures.

Scripts/features.py

@@ -45,13 +45,17 @@ def rule(liga):
                  [LIG   f i] LIG
                  [ f    f i] LIG }
     """
+    rules = []
     # standard ignores:
     #   ignore sub {0} {0}' {1};
     #   ignore sub {0}' {1} {1};
-    rules = [
+    if tuple(liga) not in skip_ignores:
+        rules.extend(
+            [
                 ignore(prefix=liga[:1], head=liga[0], suffix=liga[1:]),
                 ignore(head=liga[0], suffix=(liga[1:] + [liga[-1]])),
             ]
+        )
 
     # careful with repeats:
     # #133 ->->->->, /**/**/**/, etc.
@@ -220,5 +224,14 @@ ignore_prefixes = [
 ]
 
 
+# DO NOT generate ignores at all
+skip_ignores = {
+    # # <<*>> <<+>> <<$>>
+    # ("less", "asterisk", "greater"),
+    # ("less", "plus", "greater"),
+    # ("less", "dollar", "greater"),
+}
+
+
 def indent(text, prefix):
     return '\n'.join(prefix + line for line in text.split('\n'))