docs: restructuring images directory

see also previous commit
Also updates `scripting_intro.rst` to use literal includes, and uses individual image outputs to avoid the intermediary `.tex` file to join them all.

docs/source/_images/internals/overview_flow.tex

@@ -0,0 +1,37 @@
+\documentclass[12pt,tikz]{standalone}
+\pdfinfoomitdate 1
+\pdfsuppressptexinfo 1
+\pdftrailerid{}
+\usepackage[utf8]{inputenc}
+\usepackage{amsmath}
+\usepackage{pgfplots}
+\usepackage{tikz}
+\usetikzlibrary{shapes.geometric}
+\pagestyle{empty}
+
+\begin{document}
+\begin{tikzpicture}
+	\tikzstyle{process} = [draw, fill=green!10, rectangle, minimum height=3em, minimum width=10em, node distance=15em]
+	\tikzstyle{data} = [draw, fill=blue!10, ellipse, minimum height=3em, minimum width=7em, node distance=15em]
+	\node[process] (vlog) {Verilog Frontend};
+	\node[process, dashed, fill=green!5] (vhdl) [right of=vlog] {VHDL Frontend};
+	\node[process] (ilang) [right of=vhdl] {RTLIL Frontend};
+	\node[data] (ast) [below of=vlog, node distance=5em, xshift=7.5em] {AST};
+	\node[process] (astfe) [below of=ast, node distance=5em] {AST Frontend};
+	\node[data] (rtlil) [below of=astfe, node distance=5em, xshift=7.5em] {RTLIL};
+	\node[process] (pass) [right of=rtlil, node distance=5em, xshift=7.5em] {Passes};
+	\node[process] (vlbe) [below of=rtlil, node distance=7em, xshift=-13em] {Verilog Backend};
+	\node[process] (ilangbe) [below of=rtlil, node distance=7em, xshift=0em] {RTLIL Backend};
+	\node[process, dashed, fill=green!5] (otherbe) [below of=rtlil, node distance=7em, xshift=+13em] {Other Backends};
+
+	\draw[-latex] (vlog) -- (ast);
+	\draw[-latex] (vhdl) -- (ast);
+	\draw[-latex] (ast) -- (astfe);
+	\draw[-latex] (astfe) -- (rtlil);
+	\draw[-latex] (ilang) -- (rtlil);
+	\draw[latex-latex] (rtlil) -- (pass);
+	\draw[-latex] (rtlil) -- (vlbe);
+	\draw[-latex] (rtlil) -- (ilangbe);
+	\draw[-latex] (rtlil) -- (otherbe);
+\end{tikzpicture}
+\end{document}