Unicode input: When searching by name search for prefix matches as well as whole word matches

So now hori matches both "hori" and "horizontal". Switched to a
prefix-trie internally.

kittens/unicode_input/main.py

@@ -56,7 +56,7 @@ def name(cp):
 @lru_cache(maxsize=256)
 def codepoints_matching_search(parts):
     ans = []
-    if parts and parts[0]:
+    if parts and parts[0] and len(parts[0]) > 1:
         codepoints = points_for_word(parts[0])
         for word in parts[1:]:
             pts = points_for_word(word)