Emacs movement bindings

When using pgcli with emacs bindings, I'll often have a long multi-line query

> SELECT a, max(b), c
FROM t
WHERE ...
GROUP BY a, c
...

when point is in the middle of the query, I don't know how to get to the start of the prompt other than pressing up-arrow several times. Perhaps this was different before https://github.com/prompt-toolkit/python-prompt-toolkit/issues/106, I'm not sure.

One option I can think of is to introduce the emacs paragraph and sentence bindings.

https://www.gnu.org/software/emacs/manual/html_node/emacs/Paragraphs.html
https://www.gnu.org/software/emacs/manual/html_node/emacs/Sentences.html

there are also a bunch more useful movement bindings

https://www.gnu.org/software/emacs/manual/html_node/emacs/Moving-Point.html

I'm not sure where they'd all go given the extraction of some readline bindings discussed in https://github.com/prompt-toolkit/python-prompt-toolkit/issues/56#issuecomment-234368457.

No file, test, or entry point is named. Start by locating the existing Emacs and extracted readline bindings, then review the linked prompt-toolkit discussions; done should mean users can move to the start of a multi-line query and use the selected useful Emacs movement bindings.