Docs: Use underscores in kitten document filenames

docs/kittens/unicode_input.rst

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+Unicode input
+================
+
+You can input unicode characters by name, hex code, recently used and even an editable favorites list.
+Press :sc:`input_unicode_character` to start the unicode input widget, shown below.
+
+.. figure:: ../screenshots/unicode.png
+    :alt: A screenshot of the unicode input widget
+    :align: center
+    :width: 100%
+
+    A screenshot of the unicode input widget
+
+In :guilabel:`Code` mode, you enter a unicode character by typing in the hex code for the
+character and pressing enter, for example, type in ``2716`` and press enter to get
+✖. You can also choose a character from the list of recently used characters by
+typing a leading period and then the two character index and pressing Enter.
+The up and down arrow keys can be used to choose the previous and next unicode
+symbol respectively.
+
+In :guilabel:`Name` mode you instead type words from the character name and use
+the arrow keys/tab to select the character from the displayed matches. You can
+also type a space followed by a period and the index for the match if you don't
+like to use arrow keys.
+
+You can switch between modes using either the keys :kbd:`F1` ... :kbd:`F4` or
+:kbd:`Ctrl+1` ... :kbd:`Ctrl+4` or by pressing :kbd:`Ctrl+[` and :kbd:`Ctrl+]`
+or by pressing :kbd:`Ctrl+Tab` and :kbd:`Ctrl+Shift+Tab`.
+
+
+.. include:: ../generated/cli-kitten-unicode_input.rst