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/intro/acknowledgements.tex

@@ -1,6 +1,6 @@
 This book would not have been possible without your help.
 
-With all your donations I have been able to focus on finishing
+With all your donations I~have been able to focus on finishing
 this book. Your continuous support allows me to focus
 on improving this book even more.
 
@@ -31,4 +31,4 @@ Thank you very much for your support!\\
   columns/Name/.style={column type=l,string type},
   every head row/.style={before row=\toprule, after row=\midrule\endhead},
   every last row/.style={after row=\bottomrule}
-  ]{supporters.csv}
+  ]{supporters.csv}