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/mqtt.h/items.json

@@ -0,0 +1,80 @@
+{
+    "items": [
+        {
+            "type": "markdown",
+            "name": "intro.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_set_protocol_mqtt.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_send_mqtt_handshake.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_send_mqtt_handshake_opt.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_publish.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_subscribe.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_unsubscribe.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_disconnect.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_connack.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_puback.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_pubrec.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_pubrel.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_pubcomp.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_suback.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_unsuback.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_ping.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_pong.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_mqtt_next_subscribe_topic.md"
+        },
+        {
+            "type": "markdown",
+            "name": "struct_mg_mqtt_topic_expression.md"
+        }
+    ]
+}