Editing mode fix and documentation scrolling

[joguSD]

Prompt toolkit deprecated setting the editing mode via the enable_vi_mode kwarg on key manager creation. The editing mode is now directly passed to the Application instantiation based on the bool instead.

Additionally, I've enabled mouse support to switch between the default and docs buffers on click and allowed for scrolling in the docs buffer. I've also added a keybinding on F9 to switch between the buffers. I'm not sure which key is best to toggle back and forth, perhaps there are some standards that vim/emacs have that we could bind this to instead.
Fix for #74

Note: Enabling mouse support in prompt_toolkit seems to have the side effect that the terminals built in text highlighting/selection no longer works. I verified this behavior by looking at pyvim which also does the same thing. While switching between the buffers with mouse clicks and scrolling the docs with the scroll wheel is very natural, losing text selection might not be the best customer experience.

@jamesls @JordonPhillips

[JordonPhillips]

I'm 0 on enabling mouse mode. I don't know that mouse scrolling is really what we're looking for. On the other hand, the very limited subset of vim bindings doesn't seem to have the capability to page up and down, so there may be no other way.

I like the binding for switching windows (since changing buffers also appears to be unsupported), but I think it needs an entry on the help line.

[donnemartin]

Related issues:

• How do I navigate the documentation panel? #74
• Unable to scroll documentation pane #159

[jamesls]

Seems fine, I like being able to click on the doc buffer to scroll (though I don't think I'd actually scroll with my mouse). Could you update the docs as well?

[joguSD]

@jamesls Yeah, I can update the docs. It's also worth mentioning that clicking to switch buffers isn't required to scroll the buffer. Enabling mouse support and hovering over the buffer while scrolling will send the scroll events to that buffer even if it's not focused. Clicking to switch buffers, as well as the F9 hotkey enable the vim/emacs keybindings to be applied to the docs buffer.