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-wheat-sourdough-starter-process.tex

@@ -4,9 +4,9 @@
 \begin{tikzpicture}[node distance = 3cm, auto]
   \node [decision] (init) {\footnotesize Starter last fed within 3 days?};
   \node [block, right of=init, node distance=4cm] (feed_no_branch)
-    {\footnotesize Feed starter twice. 48 hours before and 6-12 hours before};
+    {\footnotesize Feed starter twice. 48 hours before and 6--12 hours before};
   \node [block, below of=feed_no_branch, node distance=3cm] (feed_yes_branch)
-    {\footnotesize Feed starter once 6-12 hours before making dough};
+    {\footnotesize Feed starter once 6--12 hours before making dough};
   \node [block, right of=feed_no_branch, node distance=6cm] (high_ratio)
     {\footnotesize Use a 1:10:10 ratio. 10g starter, 100g flour, 100g water};
   \node [block, right of=feed_yes_branch, node distance=3cm] (low_ratio)