Add switch_to_persian_key and switch_to_english_key

[sina-devel]

Converts English chars to their equivalent Persian char on keyboard.

"sghl ]i ofv ?".switch_to_persian_key(); // "سلام چه خبر ؟"

Converts Persian chars to their equivalent English char on keyboard.

"اثغ صاشفس عح ؟".switch_to_english_key(); // "hey whats up ?"