Added simpler .hist example

[jbednar]

The Histogram page in the Reference Gallery didn't have a simple example of using '.hist()', which is typically much more convenient than the complex example shown. Added this simple example:

Works fine for Bokeh, but in mpl there is a strange colormap:

The last example on that page (not really modified in this PR) is also aligned and sized very strangely for matplotlib, though it works fine for bokeh:

[jlstevens]

That is a worthwhile example to add. Best we wait to see which of those matplotlib bugs can be fixed before merging.

[philippjfr]

Will see, dealing with adjoints more generally in matplotlib has been a longstanding issue (see #1033).

[jlstevens]

@philippjfr Should we merge despite the weird matplotlib output?

[philippjfr]

I'll see if I can deal with the wrong colormapping at least. Doubt I'll be able to fix the sizing issue easily.

[philippjfr]

@jbednar Would you mind updating this PR by setting an explicit range for the x and y dimensions? For now matplotlib won't normalize the points and histogram together so you end up with different scales.

[jbednar]

It sounds like you know what's needed; can you just push what you suggest to the PR?

[philippjfr]

Done. @jlstevens ready to merge when tests pass.

[jlstevens]

Looks good and the tests are passing. Merging.