Function renderTimeSignature

Render a time signature to braille music notation.

Per Music Braille Code 2015, Table 7 / Par. 7.1: number sign + numerator in UPPER-cell digits + denominator in LOWER-cell digits.

• 4/4 → ⠼⠙⠲ (number sign + upper 4 + lower 4)
• 3/4 → ⠼⠉⠲ (number sign + upper 3 + lower 4)
• 6/8 → ⠼⠋⠦ (number sign + upper 6 + lower 8)
• 12/8 → ⠼⠁⠃⠦ (number sign + upper 1,2 + lower 8)