⌂ Metronome marks with more options

If you need, in metronome marks:

• change the default = sign to other symbol, you can use the property tempoEquationText.
• change the default - sign between tempo values (e.g. 100-120) to, say, 100~120, you can use the property tempoBetweenText.
• hide the default parenthesis in metronome marks, you can set the property tempoHideParenthesis as true.
• change the color of the tempo value, you can use the property tempoNumberColor.

• the text (e.g., Allegro) is a bit larger than the default of Lilypond.
• the note (e.g., ♪) is a bit smaller than the default of Lilypond.

This snippet is based on a snippet by Arnold Theresius. The original snippet create a formatter called format-metronome-markup-approx, and the default value to tempoEquationText in that snippet is "≈". I changed back this default to Lilypond default, and added the tempoBetweenText property. Also, I changed the sizing of some elements, as described above.