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.h/mg_set_protocol_dns.md

@@ -0,0 +1,19 @@
+---
+title: "mg_set_protocol_dns()"
+decl_name: "mg_set_protocol_dns"
+symbol_kind: "func"
+signature: |
+  void mg_set_protocol_dns(struct mg_connection *nc);
+---
+
+Attach built-in DNS event handler to the given listening connection.
+
+DNS event handler parses incoming UDP packets, treating them as DNS
+requests. If incoming packet gets successfully parsed by the DNS event
+handler, a user event handler will receive `MG_DNS_REQUEST` event, with
+`ev_data` pointing to the parsed `struct mg_dns_message`.
+
+See
+[captive_dns_server](https://github.com/cesanta/mongoose/tree/master/examples/captive_dns_server)
+example on how to handle DNS request and send DNS reply. 
+