[proposal] easy triplets and tuplets - was [talk] easy tuplets

[Ian Hulin]

This is a proposal to move the triplet/tuplet discussion forward.

There will be new commands to supplement (or eventually replace) the
current \times command.

1. \tuplet n/m {<music expression>}
%  does what \times does, but not so easily confused with \time
%  command.
2. \triplet {<music expression>} % shorthand for current
%  \times 2/3 command
3. \duplet {<music expression} % shorthand for current
%  \times 3/2 command
4. \quadruplet {<music expression} % shorthand for current
%  \times 6/4 command
5. \sextuplet {<music expression} % shorthand for current
%  \times 4/6 command

At the moment the design is deliberately restricted to providing
shortcrust for the \times commands with 2:3 and 3:2 ratios expressed in
the n/m rational parameter.

This should be relatively easy to implement by adding declarations to
music-functions-init.ly.

Questions:
1. Should the new \tuplet retain the \times meaning of the fraction,
i.e. \tuplet 2/3 {c8 c c} uses 2/3 because that's what you'd use if you
were just using durations: c8*2/3 c c , or
invert it as \tuplet 3/2 {c8 c c} because that reflects better the
"three notes in the time of two" definition of a triplet.

2. Should the \tuplet command attempt to validate the length of the
incoming music expression?  I.e. add up the lengths of the constituent
notes in the music expression, and see if it would be a valid
note-length once multiplied (or divided depending on decision for 1.
above) the fraction.

Cheers,

Ian Hulin