fix(history): respect zdotdir config (#83)

closes #82

Also added a `HISTFILE` so it always reads the correct file that the
shell is pointing to

Is there a `HISTFILE`? If so, use it
If it's Zsh: Is there a `ZDOTDIR`? Use `ZDOTDIR/.zsh_history`
If it's Fish: Is there an `XDG_DATA_HOME`? Use
`XDG_DATA_HOME/fish/fish_history`
If none of them are present, revert to the default `$HOME/...`

integration/shell/adapter.go

@@ -125,6 +125,14 @@ func GetFishConfigDir() string {
 	return filepath.Join(home, ".config", "fish")
 }
 
+func GetFishDataDir() string {
+	if xdg := os.Getenv("XDG_DATA_HOME"); xdg != "" {
+		return filepath.Join(xdg, "fish")
+	}
+	home, _ := os.UserHomeDir()
+	return filepath.Join(home, ".local", "share", "fish")
+}
+
 func ScanPosixAliases(files []string) map[string]string {
 	aliases := make(map[string]string)
 	home, err := os.UserHomeDir()