\tempo feature requests

[Malte Meyn]

Hi list,

could the snippets http://lsr.di.unimi.it/LSR/Item?id=1008 and
http://lsr.di.unimi.it/LSR/Item?id=574 become part of LilyPond? Maybe 
with all or some of the following additions/changes:

Snippet 1008:
• To make it backwards-compatible don’t change the default sizes; maybe 
introduce a grob property which scales the notes.
• IMO coloring (only) the number is very special and could be omitted.
• Offer three values for tempoShowParentheses: #t, #f and 'if-no-text 
(the latter mimicking the current default behaviour).
• Add ASCII/scheme symbol shorthands for non-ASCII symbols like ≈ and ≙.

Snippet 574:
• Either introduce a new command \tempoEquiv which takes two durations
• or extend \tempo. Suggested backwards-compatible syntax:
        \tempo [string] [duration [~ duration] [= number [- number]]]
Examples:
        \tempo "Allegro"
        \tempo 4 = 120 - 126
        \tempo 4 ~ 2
        \tempo "L’istesso tempo" 4 ~ 4. = 120-126
The latter should output “L’istesso tempo (𝅘𝅥 = 𝅘𝅥𝅭 = 120 – 126)”
• Add MIDI support: if a number is given, use this. If only an 
equivalence like 4 ~ 4. is given, compute the new tempoWholesPerMinute 
from the old one. (Is this possible?)

Any opinions?

Cheers,
Malte