Doxygen: rename all .dox files to end with .md

Using a standard ending here will let other tools that expect
markdown understand our output here.

This commit was automatically generated with:

   for fn in $(find src -name '*.dox'); do \
      git mv "$fn" "${fn%.dox}.md"; \
   done

1 files changed, 6 insertions, 0 deletions

diff --git a/src/app/config/app_config.md b/src/app/config/app_config.md
new file mode 100644
index 0000000000..b359ce77f6
--- /dev/null
+++ b/src/app/config/app_config.md
@@ -0,0 +1,6 @@
+@dir /app/config
+@brief app/config: Top-level configuration code
+
+Refactoring this module is a work in progress, see
+[ticket 29211](https://trac.torproject.org/projects/tor/ticket/29211).
+