Remove old docs, rename docs_new to docs

It would be probably good idea to also remove tools/docgen.py and
asciidoc.mk, but asciidoc.mk is still mentioned under `cloud/doc`, which
may contain some useful info which we'll need at least to review before
removing.

PUBLISHED_FROM=faf454d4c52a2f07ea8ac084cf0bd11a0c9c9b3b

docs/c-api/dns-server.h/mg_dns_send_reply.md

@@ -0,0 +1,19 @@
+---
+title: "mg_dns_send_reply()"
+decl_name: "mg_dns_send_reply"
+symbol_kind: "func"
+signature: |
+  void mg_dns_send_reply(struct mg_connection *nc, struct mg_dns_reply *r);
+---
+
+Send a DNS reply through a connection.
+
+The DNS data is stored in an IO buffer pointed by reply structure in `r`.
+This function mutates the content of that buffer in order to ensure that
+the DNS header reflects size and flags of the mssage, that might have been
+updated either with `mg_dns_reply_record` or by direct manipulation of
+`r->message`.
+
+Once sent, the IO buffer will be trimmed unless the reply IO buffer
+is the connection's send buffer and the connection is not in UDP mode. 
+