added lyrics store feature

Modified the function `printLyrics()` into two different functions, one to download and store the lyrics(`downloadLyrics()`) and one to display it(`printLyrics()`).

Currently the lyrics is stored as a `.lrc` file with the same name as the music file, in the same directory.

I also have corrected Issue#1(where the contents of parsed xml cannot be read), because this feature would not work without that.