Refactor Mongoose documentation

PUBLISHED_FROM=e9a4e5c7b4a1d03b93a2a79e29de19e60e919929

docs/intro.md

@@ -3,9 +3,11 @@ title: Mongoose - a networking library
 color: '#1D6482'
 repo: https://github.com/cesanta/mongoose
 items:
-  - { type: file, name: overview.md }
-  - { type: dir, name: usage-example }
-  - { type: dir, name: design-concept }
-  - { type: dir, name: build-options }
-  - { type: flat, name: c-api }
+  - { name: overview }
+  - { name: http }
+  - { name: mqtt }
+  - { name: dns }
+  - { name: coap }
+  - { name: dns_resolver }
+  - { name: core }
 ---