Jump to bookmark list

[ds2606]

Description

When I open NERDTree, I'm usually dropped somewhere in the middle of a directory listing. I'd like to quickly navigate to my bookmarks to select a bookmarked directory.

There are bindings like ? for help, p for the parent, why not have a binding b to jump to the bookmark list?

Right now, I have to manually scroll up to get there every time. b is currently unused, and seems like a natural fit.

[ds2606]

Documenting my progress in this comment:

• It seems that there's a workaround with the keystring BB (closes/opens bookmarks, redrawing the cursor there) but seems like this would be better as built-in functionality.
• I'm learning how to use the NERDTreeKeyMapAPI based on information in this blog post.
• I've found the built-in function NERDTree.CursorToBookmarkTable() in nerdtree.vim, but currently can't find a way to expose it to the external script.
• This didn't seem doable with an external script and the mapping API, so I built in the change and submitted a PR (fix typo #1306 )

Addressed in #1306