New customizable geiser-repl-query-on-kill-p

In case you don't care about killing live REPLs...
Fix for evaluations returning no result

Such as (values), which produce a retort of the form ((result) ...),
which has nothing wrong in it!  Thanks to Diogo.
New flag to automatically start REPLs when geiser-mode is activated

When no live REPL is found, of course.  The flag's imaginatively
called geiser-mode-start-repl-p.
Documentation for the latest changes
Hide auto-started REPL

I'm not convinced that this is the right thing, and the effect is a
bit ugly (we use save-window-excursion), but maybe this is the correct
thing to do for users that want auto-start.
Evaluate last expression to buffer with a prefix

Use a prefix before pressing C-x C-e to print the result of evaluating
the expression before mark to the current buffer.
Simplifications to previous patch
A bit of documentation for the previous patches