Docs are generated for Mongoose

Comments in headers are changed a bit: removed adoc-specific stuff,
markdown is used instead

PUBLISHED_FROM=9242cce85cc52a47a197d377e7e23804721a6bb5

docs/c-api/net.h/struct_mg_str.md

@@ -0,0 +1,13 @@
+---
+title: "struct mg_str"
+decl_name: "struct mg_str"
+symbol_kind: "struct"
+signature: |
+  struct mg_str {
+    const char *p; /* Memory chunk pointer */
+    size_t len;    /* Memory chunk length */
+  };
+---
+
+Describes chunk of memory 
+