BitmapText docs update and new line character

Style parameter is not optional for BitmapText (it requires at least font name). Alignment is optional.
Also different operating systems uses different new line characters. Now PIXI supports all of them.
> \n is used as an end-of-line terminator in Unix text files
> \r is used as an end-of-line terminator in Mac text files
> \r\n (ie both) are used to terminate lines in Windows and DOS text files.