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, 18 insertions, 0 deletions

diff --git a/src/core/core.md b/src/core/core.md
new file mode 100644
index 0000000000..8ecc43eaae
--- /dev/null
+++ b/src/core/core.md
@@ -0,0 +1,18 @@
+@dir /core
+@brief core: main loop and onion routing functionality
+
+The "core" directory has the central protocols for Tor, which every
+client and relay must implement in order to perform onion routing.
+
+It is divided into three lower-level pieces:
+
+   - \refdir{core/crypto} -- Tor-specific cryptography.
+
+   - \refdir{core/proto} -- Protocol encoding/decoding.
+
+   - \refdir{core/mainloop} -- A connection-oriented asynchronous mainloop.
+
+and one high-level piece:
+
+   - \refdir{core/or} -- Implements onion routing itself.
+