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.

kitty_tests/unicode_input.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
+
+
+from . import BaseTest
+
+
+class TestUnicodeInput(BaseTest):
+
+    def test_word_trie(self):
+        from kittens.unicode_input.unicode_names import codepoints_for_word
+
+        def matches(a, *words):
+            ans = codepoints_for_word(a)
+            for w in words:
+                ans &= codepoints_for_word(w)
+            return set(ans)
+
+        self.ae(matches('horiz', 'ell'), {0x2026, 0x22ef, 0x2b2c, 0x2b2d, 0xfe19})
+        self.ae(matches('horizontal', 'ell'), {0x2026, 0x22ef, 0x2b2c, 0x2b2d, 0xfe19})
+        self.assertFalse(matches('sfgsfgsfgfgsdg'))