docs: redo content generation for mdbook and manual

manpages can be rendered using the markdown output of mdbook, the rest
of the manual can generated out of the main doc/manual source tree. we
still use lowdown to actually render manpages instead of eg mdbook-man
because lowdown does generate reasonably good manpages (though that is
also somewhat debatable, but they're a lot better than mdbook-man).

doing this not only lets us drastically simplify the lowdown pipeline,
but also remove all custom {{#include}} handling since now mdbook does
all of it, even for the manpage builds. even the lowdown wrapper isn't
entirely necessary because lowdown can take all wrapper arguments with
command line flags rather than bits of input file content.

This also implements running mdbook in Meson, in order to generate the
manpages. The mdbook outputs are also installed in the usual location.

Co-authored-by: Qyriad <qyriad@qyriad.me>

Change-Id: I60193f9fd0f15d48872f071af35855cda2a0f40b

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libutil/config.hh b/src/libutil/config.hh
index 01e1239b3..fb433c607 100644
--- a/src/libutil/config.hh
+++ b/src/libutil/config.hh
@@ -436,7 +436,7 @@ struct ExperimentalFeatureSettings : Config {
 
           The following experimental features are available:
 
-          {{#include experimental-features-shortlist.md}}
+          {{#include @generated@/command-ref/experimental-features-shortlist.md}}
 
           Experimental features are [further documented in the manual](@docroot@/contributing/experimental-features.md).
         )"};