Use Siunitx package for dealing with units (#129)

It is complicated :
[1] The International System of Units (si), https://www.bipm.org/en/
measurement-units/.
[2] International System of Units from nist, http://physics.nist.gov/cuu/Units/
index.html.

And one will never get it right (space or not, half-space?) nor
consistent so using that instead.

I am not sure how times and hours, when to write digits and when in
letter so I did not change much..

Did not touch the tables as ebooks on github actions seems to break when
you look at them funny.

Co-authored-by: Cedric <ced@awase.ostal>

book/history/sourdough-history.tex

@@ -2,7 +2,7 @@ Sourdough has been made since ancient times. The exact origins of fermented
 bread are, however, unknown. One of the most ancient preserved
 sourdough breads has been excavated in Switzerland.
 However, based on recent research, some scientists speculate that sourdough
-bread had already been made in 12000 BC in ancient Jordan~\cite{jordan+bread}.
+bread had already been made in \num{12000}~BC in ancient Jordan~\cite{jordan+bread}.
 
 \begin{figure}[h]
   \includegraphics[width=\textwidth]{einkorn-crumb}
@@ -78,8 +78,8 @@ what I~describe as the 150 lost years of bread making. In 1879
 the first machines and centrifuges were developed to centrifuge
 pure yeast. This yeast would be extracted from batches of sourdough.
 The pure yeast would prove to be excellent and turbocharged
-at leavening bread doughs. What would previously take 10 hours
-to leaven a bread dough could now be done within 1 hour.
+at leavening bread doughs. What would previously take 10~hours
+to leaven a bread dough could now be done within 1~hour.
 The process became much more efficient. During World~War~II
 the first packaged dry yeast was developed. This would ultimately
 allow bakeries and home bakers to make bread much faster.