Add sub-word actions (#3997)

Add `backward-subword`, `forward-subword`, `kill-subword`, `backward-kill-subword` actions.

Author: masmu

man/man1/fzf.1

@@ -1807,7 +1807,9 @@ A key or an event can be bound to one or more of the following actions.
     \fBbackward\-char\fR                \fIctrl\-b  left\fR
     \fBbackward\-delete\-char\fR         \fIctrl\-h ctrl\-bspace bspace\fR
     \fBbackward\-delete\-char/eof\fR     (same as \fBbackward\-delete\-char\fR except aborts fzf if query is empty)
+    \fBbackward\-kill\-subword\fR
     \fBbackward\-kill\-word\fR           \fIalt\-bs\fR
+    \fBbackward\-subword\fR
     \fBbackward\-word\fR                \fIalt\-b   shift\-left\fR
     \fBbecome(...)\fR                  (replace fzf process with the specified command; see below for the details)
     \fBbeginning\-of\-line\fR            \fIctrl\-a  home\fR
@@ -1847,10 +1849,12 @@ A key or an event can be bound to one or more of the following actions.
     \fBexecute\-silent(...)\fR          (see below for the details)
     \fBfirst\fR                        (move to the first match; same as \fBpos(1)\fR)
     \fBforward\-char\fR                 \fIctrl\-f  right\fR
+    \fBforward\-subword\fR
     \fBforward\-word\fR                 \fIalt\-f   shift\-right\fR
     \fBignore\fR
     \fBjump\fR                         (EasyMotion-like 2-keystroke movement)
     \fBkill\-line\fR
+    \fBkill\-subword\fR
     \fBkill\-word\fR                    \fIalt\-d\fR
     \fBlast\fR                         (move to the last match; same as \fBpos(\-1)\fR)
     \fBnext\-history\fR                 (\fIctrl\-n\fR on \fB\-\-history\fR)

src/actiontype_string.go

@@ -1663,6 +1663,8 @@ func parseActionList(masked string, original string, prevActions []*action, putA
 			appendAction(actBackwardDeleteCharEof)
 		case "backward-word":
 			appendAction(actBackwardWord)
+		case "backward-subword":
+			appendAction(actBackwardSubWord)
 		case "clear-screen":
 			appendAction(actClearScreen)
 		case "delete-char":
@@ -1683,6 +1685,8 @@ func parseActionList(masked string, original string, prevActions []*action, putA
 			appendAction(actForwardChar)
 		case "forward-word":
 			appendAction(actForwardWord)
+		case "forward-subword":
+			appendAction(actForwardSubWord)
 		case "jump":
 			appendAction(actJump)
 		case "jump-accept":
@@ -1691,6 +1695,8 @@ func parseActionList(masked string, original string, prevActions []*action, putA
 			appendAction(actKillLine)
 		case "kill-word":
 			appendAction(actKillWord)
+		case "kill-subword":
+			appendAction(actKillSubWord)
 		case "unix-line-discard", "line-discard":
 			appendAction(actUnixLineDiscard)
 		case "unix-word-rubout", "word-rubout":
@@ -1699,6 +1705,8 @@ func parseActionList(masked string, original string, prevActions []*action, putA
 			appendAction(actYank)
 		case "backward-kill-word":
 			appendAction(actBackwardKillWord)
+		case "backward-kill-subword":
+			appendAction(actBackwardKillSubWord)
 		case "toggle-down":
 			appendAction(actToggle, actDown)
 		case "toggle-up":