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/util.h/mg_base64_encode.md

@@ -0,0 +1,12 @@
+---
+title: "mg_base64_encode()"
+decl_name: "mg_base64_encode"
+symbol_kind: "func"
+signature: |
+  void mg_base64_encode(const unsigned char *src, int src_len, char *dst);
+---
+
+Base64-encode chunk of memory `src`, `src_len` into the destination `dst`.
+Destination has to have enough space to hold encoded buffer.
+Destination is '\0'-terminated. 
+