add rhombic polihedra (#1022)

* adds rhombi faces, two rhombic dodecahedra, partial tricontahedron.

the rhombi faces are four: right or left leaning, golden or square-of-two
ratio between diagonals.  there's the "type 1" rhombic dodecahedron, a
Catalan solid having as faces square-of-two rhombi, the "type 2" rhombic
dodecahedron having as faces golden rhombi, and about half the faces needed
to build a golden rhombic tricontahedron.

* fixing tricontahedron to use golden rhombi

* addresses #1020, refinements on flat golden rhombic dodecahedron

* addresses #1020, added "type 1" specification

* reviewing, adding to the manual page.

doc/generic/pgf/text-en/pgfmanual-en-library-folding.tex

@@ -188,6 +188,26 @@ \section{Paper-Folding Diagrams Library}
     %
 \end{pictype}
 
+\begin{pictype}{dodecahedron rhombic folding}{}
+    A rhombic dodecahedron, based on square-of-two rhombi.
+    %
+\begin{codeexample}[preamble={\usetikzlibrary{folding}}]
+\tikz \pic [folding line length=6mm, numbered faces, transform shape]
+  { dodecahedron rhombic folding };
+\end{codeexample}
+    %
+\end{pictype}
+
+\begin{pictype}{dodecahedron golden folding}{}
+    An alternative rhombic dodecahedron, flat laying, based on golden rhombi.
+    %
+\begin{codeexample}[preamble={\usetikzlibrary{folding}}]
+\tikz \pic [folding line length=6mm, numbered faces, transform shape]
+  { dodecahedron golden folding };
+\end{codeexample}
+    %
+\end{pictype}
+
 \begin{pictype}{cuboctahedron folding}{}
     A folding of a cuboctahedron.
     %