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/mg_mgr_init.md

@@ -0,0 +1,15 @@
+---
+title: "mg_mgr_init()"
+decl_name: "mg_mgr_init"
+symbol_kind: "func"
+signature: |
+  void mg_mgr_init(struct mg_mgr *mgr, void *user_data);
+---
+
+Initialize Mongoose manager. Side effect: ignores SIGPIPE signal.
+`mgr->user_data` field will be initialized with `user_data` parameter.
+That is an arbitrary pointer, where user code can associate some data
+with the particular Mongoose manager. For example, a C++ wrapper class
+could be written, in which case `user_data` can hold a pointer to the
+class instance. 
+