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, 8 insertions, 0 deletions

diff --git a/src/feature/hs/feature_hs.md b/src/feature/hs/feature_hs.md
new file mode 100644
index 0000000000..299d07e014
--- /dev/null
+++ b/src/feature/hs/feature_hs.md
@@ -0,0 +1,8 @@
+@dir /feature/hs
+@brief feature/hs: v3 (current) onion service protocol
+
+This directory implements the v3 onion service protocol,
+as specified in
+[rend-spec-v3.txt](https://gitweb.torproject.org/torspec.git/tree/rend-spec-v3.txt).
+
+