Add 'put' action for putting the character to the prompt

fzf --bind 'space:preview(date)+put'

Close #2456

man/man1/fzf.1

@@ -860,6 +860,7 @@ A key or an event can be bound to one or more of the following actions.
     \fBpreview-top\fR
     \fBprevious-history\fR          (\fIctrl-p\fR on \fB--history\fR)
     \fBprint-query\fR               (print query and exit)
+    \fBput\fR                       (put the character to the prompt)
     \fBrefresh-preview\fR
     \fBreload(...)\fR               (see below for the details)
     \fBreplace-query\fR             (replace query string with the current selection)