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_open.md

@@ -0,0 +1,14 @@
+---
+title: "mg_open()"
+decl_name: "mg_open"
+symbol_kind: "func"
+signature: |
+  int mg_open(const char *path, int flag, int mode);
+---
+
+Open the given file and return a file stream.
+
+`path` should be UTF8 encoded.
+
+Return value is the same as for the `open()` syscall. 
+