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_set_ssl.md

@@ -0,0 +1,19 @@
+---
+title: "mg_set_ssl()"
+decl_name: "mg_set_ssl"
+symbol_kind: "func"
+signature: |
+  const char *mg_set_ssl(struct mg_connection *nc, const char *cert,
+                         const char *ca_cert);
+---
+
+Enable SSL for a given connection.
+`cert` is a server certificate file name for a listening connection,
+or a client certificate file name for an outgoing connection.
+Certificate files must be in PEM format. Server certificate file
+must contain a certificate, concatenated with a private key, optionally
+concatenated with parameters.
+`ca_cert` is a CA certificate, or NULL if peer verification is not
+required.
+Return: NULL on success, or error message on error. 
+