Use input figs (#123)

* Make figs includable in main document

Remove the capability to build them as standalone document but we can
include them in the main document.  It should simplify things down the
road.

* Replace tikx pics

* Remove figures compilation from makefile

No need to compile figs to pdf anymore, at least to build the books

* Delete svg figures from ebook build

* Create png for TikZ figures

    - Add export_figures back
    - Build a pdf from the the TikZ in standalone mode
    - Change the cleanup to deal with those changes
    - Remove trailing spaces..

* Replace centering by an environment

More LaTeX idomatic

* Increase clean_figures robustness

as we use temporary tex files (.tex.in) we can't run clean_figures twice in a
row

* Center TikZ figures

Because it looks better

* Remove png building

Seems to struggle on CI with \\\b or something, we don't absolutely need
it right now so let's get rid of it.

* Remove trgt_figures dependency for pdf and ebooks

This should not be needed now that we include the TikZ directly, only
needed for png generation.

* Revert "Remove png building"

This reverts commit fdd542de57.

This is now fine to add the code back, so that it can be debugged when
times come.

book/bread-types/bread-types.tex

@@ -125,11 +125,12 @@ baking vessels in your oven. To make a freestanding loaf more steps
 and tools are required.
 
 \begin{figure}[!htb]
+\begin{center}
   \includegraphics[width=1.0\textwidth]{free-standing-loaf.jpg}
-  \centering
   \caption{A freestanding sourdough bread. Note the incision known as an
       \emph{ear} and the oven spring clearly
   distinguish this type of bread from flatbread and loaf pan bread.}
+\end{center}
 \end{figure}
 
 Normally you mix your dough. When using wheat you make sure
@@ -164,10 +165,12 @@ few steps, you can stop buying bread forever. This works with
 any flour, including gluten-free options.
 
 \begin{figure}[!htb]
-  \includegraphics{figures/fig-process-flat-bread.pdf}
+\begin{center}
+  \input{figures/fig-process-flat-bread.tex}
   \caption{The process of making a flatbread is very simple, requiring very little effort. This
   type of bread is especially handy for busy bakers.}%
   \label{fig:flat-bread-process}
+\end{center}
 \end{figure}
 
 This is my go-to recipe that I~use to make bread whenever
@@ -198,12 +201,13 @@ warmer it is, the sooner it will be ready. If it is very cold where you live, co
 using warm water.
 
 \begin{figure}[htb!]
+\begin{center}
   \includegraphics[width=1.0\textwidth]{flat-bread-wheat}
-  \centering
   \caption{A flatbread made with purely wheat flour. The dough is drier
   at around 60 percent hydration. The drier dough is a little harder
   to mix. As wheat contains more gluten, the dough puffs up during
   the baking process.}
+\end{center}
 \end{figure}
 
 This way you should have around 11 g of sourdough ready in the evening. You will have
@@ -225,10 +229,11 @@ when getting started. You can observe the dough more easily and see when
 it is ready.
 
 \begin{figure}[htb!]
+\begin{center}
   \includegraphics[width=1.0\textwidth]{ethiopian-woman-checking-bread}
-  \centering
   \caption{An Ethiopian woman baking an \emph{injera} made using teff flour.
   The image has been provided by Charliefleurene via Wikipedia.}
+\end{center}
 \end{figure}
 
 If you used the flatbread option with less water, look at the size increase
@@ -258,11 +263,12 @@ state of my doughs.
 
 
 \begin{figure}[htb!]
+\begin{center}
   \includegraphics[width=1.0\textwidth]{injera-pancake-texture.jpg}
-  \centering
   \caption{A sourdough pancake made with teff flour. The pockets come from
   evaporated water and \ch{CO2} created by the microbes.
   The image has been provided by Lukasz Nowak via Wikipedia.}
+\end{center}
 \end{figure}
 
 If you are feeling lazy or don't have time, you could also use older sourdough starter
@@ -293,12 +299,13 @@ making a flatbread, make the dough around 1 cm thick. When using the pancake
 option, opt for around 0.1--0.5 cm depending on what you like.
 
 \begin{figure}[htb!]
+\begin{center}
   \includegraphics[width=1.0\textwidth]{einkorn-crumb.jpg}
-  \centering
   \caption{The crumb of a flatbread made with einkorn as flour. Einkorn
   is very low in gluten and thus does not trap as much \ch{CO2} as a wheat based
   dough. To make the dough fluffier use more water or consider adding
   more wheat to the mix of your dough.}
+\end{center}
 \end{figure}
 
 After 2--4 minutes flip over the pancake or flatbread. Bake it for the same