Small fixes (#155)

* Fix various typos and references or links

- Misuse of product macro the x sign did not appear
- Use macro for milligrams
- Some refes were without hyperlink for some reason ?
- confusion between section and subsections
- a little grammar.. exact value not absolute, don't think a negative
  amount of flower was ever an option :D

* Use siunitx for temperature everywhere

Apparently some files escaped my script last time, or messed up in git
merge... Anyway fixed now and should be more consistent.

* Simplify Fermentolysis table

I woudl hope this is more clear with less lines.

* Remove double bottomrule

* Fix grammar

* Use correct font familly in preface

Small corrections on font familly and extra space for signature.
TODO: I did not change the paragraph breaking but we might want to
revisit it later.

* Fix wrong percentage range

fixes https://github.com/hendricius/the-sourdough-framework/issues/156

book/flour-types/flour-types.tex

@@ -24,7 +24,7 @@ type of flour.
 In Germany, the ash content is used to describe the flours. The lab will burn
 \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
+is of type 405 then \qty{405}{\mg} of ash have remained after burning the
 flour. The more hull parts the flour has, the more minerals remain. So the
 higher the number, the closer the flour is to whole flour. The numbers are
 slightly different between each grain type. Generally though, the higher the