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/net.h/struct_mg_mgr.md

@@ -0,0 +1,21 @@
+---
+title: "struct mg_mgr"
+decl_name: "struct mg_mgr"
+symbol_kind: "struct"
+signature: |
+  struct mg_mgr {
+    struct mg_connection *active_connections;
+    const char *hexdump_file; /* Debug hexdump file path */
+  #ifndef MG_DISABLE_SOCKETPAIR
+    sock_t ctl[2]; /* Socketpair for mg_wakeup() */
+  #endif
+    void *user_data; /* User data */
+    void *mgr_data;  /* Implementation-specific event manager's data. */
+  #ifdef MG_ENABLE_JAVASCRIPT
+    struct v7 *v7;
+  #endif
+  };
+---
+
+Mongoose event manager. 
+