Add support for search history

- Add `--history` option (e.g. fzf --history ~/.fzf.history)
- Add `--history-max` option for limiting the size of the file (default 1000)
- Add `previous-history` and `next-history` actions for `--bind`
    - CTRL-P and CTRL-N are automatically remapped to these actions when
      `--history` is used

Closes #249, #251

src/constants.go

@@ -32,6 +32,9 @@ const (
 
 	// Not to cache mergers with large lists
 	mergerCacheMax int = 100000
+
+	// History
+	defaultHistoryMax int = 1000
 )
 
 // fzf events