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

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

Close junegunn#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)

src/options.go

@@ -981,6 +981,12 @@ func parseKeymap(keymap map[tui.Event][]action, str string) {
 				appendAction(actEnableSearch)
 			case "disable-search":
 				appendAction(actDisableSearch)
+			case "put":
+				if key.Type == tui.Rune && unicode.IsGraphic(key.Char) {
+					appendAction(actRune)
+				} else {
+					errorExit("unable to put non-printable character: " + pair[0])
+				}
 			default:
 				t := isExecuteAction(specLower)
 				if t == actIgnore {