[feature] Histogram chart

[stokito]

Is it possible to draw a Histogram metric like request latency?

Thank you for the library, it's saved me.

[samber]

I never tested histograms.

As a good start, please replace type: 'line' by type: 'bar'. I'm pretty confident it should work as is.

[mnutt]

Bar (and stacked bar) now work in 2.0. I'm not sure if that alone is enough to get histograms working.

[samber]

ok, thanks @mnutt for the test

i will update the doc