Hi everyone,

Given the following plot:

```
import numpy as np
from bokeh.plotting import figure, show
h, e = np.histogram(np.random.random(100), density=True)
p = figure()
p.quad(top=h, bottom=0, left=e[:-1], right=e[1:])
show(p)
```

How do I switch the position of (rotate) the plot axis, i.e. show the distribution horizontally by having the bins along the `y axis`

, and their density on the` x axis`

? Essentially, rotate the plot by 90 degrees counter-clockwise.

Thank you,

```
bokeh.__version__
'1.4.0'
```