Add --version to --help output and man page

Close #888
Close #894

man/man1/fzf.1

@@ -352,6 +352,9 @@ ncurses finder only after the input stream is complete.
 .RS
 e.g. \fBfzf --multi | fzf --sync\fR
 .RE
+.TP
+.B "--version"
+Display version information and exit
 
 .SH ENVIRONMENT VARIABLES
 .TP

src/options.go

@@ -86,6 +86,7 @@ const usage = `usage: fzf [options]
     --read0               Read input delimited by ASCII NUL characters
     --print0              Print output delimited by ASCII NUL characters
     --sync                Synchronous search for multi-staged filtering
+    --version             Display version information and exit
 
   Environment variables
     FZF_DEFAULT_COMMAND   Default command to use when input is tty