Letter spacing small caps and all uppercase titles

[tmgriffiths]

As I alluded to in the comments in fix: #115, I've ben experimenting with letterspacing the small caps and all-caps sections of the theme. There have been some issues, namely microtype cannot do fontexpansion/tracking in conjuction with xetex, it can do this with pdftex and luatex though. I intend to use the ifluatex and ifxetex packages to either use the microtype or the fontexpansion capabilities of microtypedepending on the typesetting engine. I also need to change the fontspec loading of Fira Sans if microtype is used in conjunction with lua(la)tex to include

\defaultfontfeatures{Ligatures=TeX,SmallCapsFeatures={Renderer=Basic}}

othewise the small caps don't render correcly and are turned into regular case.

What i'll probably do will end up looking something like this:

\ifxetex
   \newcommand{\myletterspacing}{\addfontfeatures{LetterSpace=6}}   
\else
   \RequirePackage[tracking=true]{microtype}
   \defaultfontfeatures{Ligatures=TeX,SmallCapsFeatures={Renderer=Basic}}
   \microtypesetup{letterspace=60}
   \newcommand{\@metropolis@letterspacing}{\lsstyle}   
\fi

\@metropolis@letterspacing can then be used wherever \MakeUppercase is used or \MakeLowercase and small caps are used.

Note: Ligatures=TeX replaces Mapping=tex-text. They do the same thing in xetex, but Ligatures=TeX makes it compatable with luatex.

[matze]

I guess this won't make it into 1.1, so we proably should push it past it.

[tmgriffiths]

Sorry @matze, I've got a thesis to finish. This got got moved a few rungs down the priority ladder. I'll pick it up again once i'm done with that.