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/flour-types/flour-types.tex

@@ -22,7 +22,7 @@ type of flour.
 \end{table}
 
 In Germany, the ash content is used to describe the flours. The lab will burn
-100 grams of flour in the oven. Then afterwards the remaining ash is extracted
+\qty{100}{\gram} of flour in the oven. Then afterwards the remaining ash is extracted
 and measured. Depending on the quantity the flour is categorized. If the flour
 is of type 405 then 405 milligrams of ash have remained after burning the
 flour. The more hull parts the flour has, the more minerals remain. So the