Fix markdown table rendering in C++ docs

This reverts commit 0bb904e10a and
re-introduces the markdown table support extension. The resulting table
by default is too wide in the "responsive" read-the-docs theme, but with
a CSS tweak it becomes readable.

Markdown tables are much easier to deal with and this way we can also
include references within the tables.

xtask/src/cppdocs.rs

@@ -62,8 +62,11 @@ pub fn generate() -> Result<(), Box<dyn std::error::Error>> {
 
     let docs_source_dir = root.join("api/sixtyfps-cpp");
     let docs_build_dir = root.join("target/cppdocs");
+    let html_static_dir = docs_build_dir.join("_static");
 
     std::fs::create_dir_all(docs_build_dir.as_path()).context("Error creating docs build dir")?;
+    std::fs::create_dir_all(html_static_dir.as_path())
+        .context("Error creating _static path for docs build")?;
 
     symlink_files_in_dir(
         docs_source_dir.join("docs"),
@@ -79,6 +82,13 @@ pub fn generate() -> Result<(), Box<dyn std::error::Error>> {
         docs_build_dir.join("README.md"),
     )?;
 
+    symlink_file(
+        ["..", "..", "..", "api", "sixtyfps-cpp", "docs", "theme_tweak.css"]
+            .iter()
+            .collect::<PathBuf>(),
+        html_static_dir.join("theme_tweak.css"),
+    )?;
+
     let pip_env =
         vec![(OsString::from("PIPENV_PIPFILE"), docs_source_dir.join("docs/Pipfile").to_owned())];