Update mongoose docs

PUBLISHED_FROM=cfd0018a5824c5ccac532558be86c17cda64ce50

docs/dns/client_example.md

@@ -2,4 +2,6 @@
 title: DNS client example
 ---
 
-TBD
+See https://github.com/cesanta/mongoose/blob/master/mongoose.c and search
+for the `mg_resolve_async_eh()` function - that is the core of
+built-in Mongoose async DNS resolver.

docs/dns_resolver/overview.md

@@ -2,4 +2,8 @@
 title: Overview
 ---
 
-TBD
+Mongoose uses non-blocking DNS resolver. For each name to be resolved,
+it first checks the `/etc/hosts` file (or, `hosts` on Windows).
+If the entry is not found there, then the `8.8.8.8` DNS server is queried.
+When IP address is found, Mongoose proceeds with making the connection
+with the resolved IP address.

docs/http/digest_auth.md

@@ -2,4 +2,15 @@
 title: Digest Authentication
 ---
 
-TBD
+Mongoose has a built-in Digest (MD5) authentication support. In order to
+enable Digest authentication, create a file `.htpasswd` in the directory
+you would like to protect. That file should be in the format that Apache's
+`htdigest` utility.
+
+You can use either Apache `htdigest` utility, or
+Mongoose pre-build binary (https://www.cesanta.com/products/binary)
+to add new users into that file:
+
+```
+mongoose -A /path/to/.htdigest mydomain.com joe joes_password
+```

docs/mqtt/client_example.md

@@ -2,4 +2,4 @@
 title: MQTT client example
 ---
 
-TBD
+See https://github.com/cesanta/mongoose-examples/tree/master/examples/mqtt_client

docs/mqtt/server_example.md

@@ -2,4 +2,4 @@
 title: MQTT server example
 ---
 
-TBD
+See https://github.com/cesanta/mongoose-examples/tree/master/examples/mqtt_broker