Some things need need to be fixed on the interfaces pages

[Christopher Heckman]

I went through the interfaces pages recently, and I found a couple of
things that need to be fixed (these is from the 2.25 version).

(1) The centered-spanner-interface page talks about using it with
MultiMeasureRest, but MultiMeasureRest isn't among the list of grobs
at the bottom that use it. (The MultiMeasureRest page doesn't mention
that it uses the centered-spanner-interface, either.)

(2) The stroke-finger-interface page says that it is for "right hand
finger instructions." Well, this isn't true if the instrument is being
played left-handed. In that case the "right hand" really is the
"picking hand" or "strumming hand."

Similarly, "left hand" should be replaced with something like
"fretting hand." (This term looks strange if you're playing a fretless
instrument. If there are any violinists out there: If you play the
violin right-handed, what is your left hand called?)

--- Christopher Carl Heckman