Change \partcombine (et al.) to \partCombine

Documentation/notation/simultaneous.itely

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 @c \version "2.20.0"
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 turning off rest merging temporarily.
 
 @node Automatic part combining
 @unnumberedsubsubsec Automatic part combining
 
 @cindex automatic part combining
 @cindex part combiner
 @cindex combining parts
 @cindex a due part
 @cindex solo part
-@funindex \partcombine
+@funindex \partCombine
 
 Automatic part combining is used to merge two separate parts of music
 onto a single staff. This can be especially helpful when typesetting
 orchestral scores.  A single @code{Voice} is printed while the two parts
 of music are the same, but in places where they differ, a second
 @code{Voice} is printed.  Stem directions are set up & down accordingly
 while Solo and @notation{a due} parts are also identified and marked
 appropriately.
 
 The syntax for automatic part combining is:
@@ skipping 71 matching lines @@
 >>
 @end lilypond
 
 
 Both arguments to @code{\partCombine} will be interpreted as separate
 @code{Voice} contexts, so if the music is being specified in relative
 mode then @emph{both} parts must contain a @code{\relative} function,
 i.e.,
 
 @example
-\partcombine
+\partCombine
   \relative @dots{} @var{musicexpr1}
   \relative @dots{} @var{musicexpr2}
 @end example
 
 @noindent
 A @code{\relative} section that encloses a @code{\partCombine} has no
 effect on the pitches of @code{@var{musicexpr1}} or
 @code{@var{musicexpr2}}.
 
 @funindex \partCombineChords
@@ skipping 241 matching lines @@
   >>
 }
 @end lilypond
 
 @seealso
 Learning Manual:
 @rlearning{Organizing pieces with variables}.
 
 Snippets:
 @rlsr{Simultaneous notes}.