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_fopen.md

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