Enable micro-typographical improvements (#191)

Few people will notice but this actually brings loads of improvements to
line breaking, handing punctuations etc.

book/sourdough.sty

@@ -12,6 +12,7 @@
 \usepackage{fontspec}
 \usepackage{calc}
 \usepackage[font={sffamily, sbseries}]{quoting}
+\usepackage{microtype}
 
 \DeclareTOCStyleEntry[numwidth=3em]{tocline}{figure}