Use X11-style key names in the feh(1) KEYS section

closes #302

man/feh.pre

@@ -1272,7 +1272,7 @@ Show next image. Selects the next image in thumbnail mode.
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 Toggle pointer visibility
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-.It p , Ao Backspace Ac , Ao Left Ac Bq prev_img
+.It p , Ao BackSpace Ac , Ao Left Ac Bq prev_img
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 Show previous image. Selects the previous image in thumbnail mode.
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@@ -1383,11 +1383,11 @@ Remove current file from filelist
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 Remove current file from filelist and delete it
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-.It Ao keypad left Ac , Ao Ctrl+Left Ac Bq scroll_left
+.It Ao keypad Left Ac , Ao Ctrl+Left Ac Bq scroll_left
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 Scroll to the left
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-.It Ao keypad right Ac , Ao Ctrl+Right Ac Bq scroll_right
+.It Ao keypad Right Ac , Ao Ctrl+Right Ac Bq scroll_right
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 Scroll to the right
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@@ -1395,7 +1395,7 @@ Scroll to the right
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 Scroll up
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-.It Ao keypad down Ac , Ao Ctrl+Down Ac Bq scroll_down
+.It Ao keypad Down Ac , Ao Ctrl+Down Ac Bq scroll_down
 .
 Scroll down.
 Note that the scroll keys work without anti-aliasing for performance reasons,