Improve typography (#120)

* Add unbreakable space before a reference or a citation

avoids ref to be put on next line or page...

* Add unbreakable space between I and verb

* Remove spacing before footnotes

Also moved it before the final sentence dots in many cases... might need
a review of what is best.  But this is a safe default choice from an
esthetic point of view.

* Improve footnotes and punctuations

Reverse order/kerning especially with sans-serif version.

* Remove manual enumerate

* Fix wording in a citation.

Reads better that way and is shorter.

* Use emph instead of italics

1) Markup semantic not style
2) Will deal with various level of empahasis
3) Was a mix of \it and \textit

* Fix usage of quotes

Also replaced some of then by \emph as it is (IMHO) more visually
pleasant.

* Captitalize before reference

* Correct dashes length

see here:
https://www.merriam-webster.com/words-at-play/em-dash-en-dash-how-to-use

* Remove space before label and homogenize caption

Apparently it can create a wrong reference, if notthing else shuts
texcheck up and cost nothing... so let's do it.

While at it adding a dot at the end of each caption.

* Add missing empty line before signature in preface

* Add a static checker target to makefile

Shall help prevent adding mistakes in new versions

book/figures/fig-liquid-starter-conversion.tex

@@ -18,6 +18,6 @@
   \path [line] (test) -- (ready_signs);
   \path [line] (ready_signs) -- node{\footnotesize no} (feed_again);
   \path [line] (ready_signs) -- node{\footnotesize yes} (last_feed);
-  \path [line] (last_feed) -- node{\footnotesize after 6-12 hours} (bread_dough);
+  \path [line] (last_feed) -- node{\footnotesize after 6--12 hours} (bread_dough);
 \end{tikzpicture}
 \end{document}