Font variants (weights, shapes) don't work#1

Using the package sourceserifpro, `\emph` or `\textit` are not working for me. Quoting from the [readme file](http://www.adobe.com/products/type/font-information/source-serif-pro-readme.html) by adobe: > One should not, however, select a base font which has no style-linked variant, and then use the bold or italic styling button. Doing so will either have no effect, or result in programmatic bolding or slanting of the base font, which will usually produce inferior screen and print results. The readme file also states that there are no extra 'fonts' for every variant but each represents a set which includes an italic variant that _should_ work. Also, the options _light_, _extralight_, _bold_, _semibold_ and _black_ are not working. The weight is always the same. Both of the problems are not existent for [`sourcesanspro`](https://github.com/silkeh/latex-sourcesanspro), which should be similar, I guess