#5405 Doc - NR 2.5 Percussion - MIDI @ref links fixes

Change link to MIDI output

section "References for percussion"

@item MIDI output is discussed in a separate section; please see
@ref{MIDI instruments}.

This should link to @ref{Creating MIDI output} instead of @ref{MIDI instruments} (appendix).
Same for "See also" links.

Change link to known problems about MIDI and percussive instruments

There are a few issues concerning MIDI support for percussion
instruments; for details please see @ref{MIDI instruments}.

@seealso
Notation Reference:
@ref{MIDI instruments},
@ref{Percussion notes}.

This should link to @ref{Using MIDI instruments} instead of @ref{MIDI instruments}.
Same also for the link in the Pitched percussion section.

[Anonymous]

Split out of https://sourceforge.net/p/testlilyissues/issues/5297/

[Anonymous]

Doc: NR - Percussion.itely fix some @ref links

Issue 5405

Changed some @ref links
from {MIDI instruments} to
{Creating MIDI output}

http://codereview.appspot.com/346910043

[Anonymous]

Passes make, make check and a full make doc.

[Anonymous]

Patch on countdown for 1st September

[Anonymous]

Patch counted down - please push.

[Anonymous]

Doc: NR - Percussion.itely fix some @ref links
author  James Lowe <pkx166h@runbox.com> 
    Sun, 26 Aug 2018 14:02:34 +0100 (14:02 +0100)
committer   James Lowe <pkx166h@runbox.com> 
    Sun, 2 Sep 2018 13:59:02 +0100 (13:59 +0100)
commit  587b14c6af69f0f0f14d8eb793d3c6c8d1729420