pandoc: allow to include other files

The following block will inlcude a second markdown file:

```{.include}
path/to/other/markdown/file.md
```

Move all used pandoc filters from the latex/ base directory into
a new pandoc/ directory.

1 files changed, 20 insertions, 0 deletions

diff --git a/pandoc/center-img.lua b/pandoc/center-img.lua
new file mode 100644
index 00000000..18782725
--- /dev/null
+++ b/pandoc/center-img.lua
@@ -0,0 +1,20 @@
+-- Based on:
+-- https://pandoc.org/lua-filters.html#center-images-in-latex-and-html-output
+-- Licensed under MIT License found at:
+-- https://github.com/TomBener/pandoc-templates/blob/05aba224519d8a2b037108948bde0d820860b786/LICENSE
+
+-- Filter images with this function if the target format is LaTeX.
+if FORMAT:match('beamer') then
+  function Image(elem)
+    -- Surround all images with the 'center' class with image-centering raw LaTeX.
+    if elem.classes[1] == "center" then
+      return {
+        pandoc.RawInline('latex', '\\hfill\\break{\\centering'),
+        elem,
+        pandoc.RawInline('latex', '\\par}')
+      }
+    else
+      return elem
+    end
+  end
+end