Added multiple fonts support

Now you can initialize multiple fonts. Font name can be specified as `fontName` attribute in XML layout. If not `fontName` specified, the first font to be initialized will be used (i.e. the default font). Font names can be extracted automatically from font file name, or set explicitly when initializing.

The code is backward-compatible, so implementations using older lib versions will not be affected.

I added another font for the sake of demonstration.