feat(pandocast): Support the lunajson parsing library as alternative

Alternative to luajson for JSON parsing.

README.md

@@ -88,9 +88,19 @@ Some *Djot* content
 
 ### Pandoc AST alternative package
 
-_Prerequisites:_ The [LuaJSON](https://github.com/harningt/luajson) module must be installed and available to your SILE environment.
-This topic is not covered here.
+_Prerequisites:_ Either [lunajson](https://github.com/grafi-tt/lunajson) or [LuaJSON](https://github.com/harningt/luajson) must be installed and available to your SILE environment. The former is recommended has no additional dependencies, and is straightforward to install:
 
+```shell
+luarocks install lunajson
+```
+
+The latter depends on the LPeg library, and this may require some additional tooling to be installed on your system (such as a C compiler, etc.). Moreover, as of 2024, the stable version has some issues, and you will neeed to install the development version instead:
+
+```shell
+luarocks install --dev luajson
+```
+
+Ready to go?
 First, using the appropriate version of Pandoc, convert your file to a JSON AST:
 
 ```shell

examples/sile-and-pandoc.dj

@@ -13,8 +13,17 @@ The following solution is still an experimental proof-of-concept, but you may gi
 ## Prerequisites
 
 Obviously, you need to have the Pandoc software installed on your system.
-You also need to have the LuaJSON module installed and available to your SILE environment.
-As of 2024, we recommend using the development version of the module, due to some issues with the current release version.
+You also need to have either the *lunajson* or *luajson* module installed and available to your SILE environment:
+
+{custom-style=CodeBlock}
+:::
+```bash
+luarocks install lunajson
+```
+:::
+
+The former is a Lua-only module, with no external dependencies.
+The other is an LPeg-based parser, and on some systems, it may require the LPeg library to be compiled and installed. Luarocks should take care of that for you, but it assumes you have the necessary development tools on your system. Moreover, as of 2024, the current release version of the module has some issues, so we recommend using the development version instead:
 
 {custom-style=CodeBlock}
 :::

inputters/pandocast.lua

@@ -582,9 +582,12 @@ function inputter.appropriate (round, filename, doc)
 end
 
 function inputter:parse (doc)
-  local has_json, json = pcall(require, "json.decode")
+  local has_json, json = pcall(require, "lunajson")
   if not has_json then
-    SU.error("The pandocast inputter requires LuaJSON's json.decode() to be available.")
+    has_json, json = pcall(require, "json.decode")
+    if not has_json then
+      SU.error("The pandocast inputter requires either luajson or lunajson to be available.")
+    end
   end
 
   local jsast = json.decode(doc)