hypertext-style priceFormatter

[liesauer]

for the small price with continuous zeros, it's much better to format the price into 0.0₃6573 or 0.0₆123 rather than showing dozens of zeros.

i have tried

priceFormatter: (price) => {
    return '0.0<sub>6</sub>123';
}

but currently it doesn't work.

hope to support this feature, and thanks for creating a such amazing chart widget.