Add mg_ prefix to mongoose sources

CL: none

PUBLISHED_FROM=d6ebe5fa88c61ae3b8569897d9b09d54610bec73

docs/c-api/mbuf.h/mbuf_insert.md

@@ -1,14 +0,0 @@
----
-title: "mbuf_insert()"
-decl_name: "mbuf_insert"
-symbol_kind: "func"
-signature: |
-  size_t mbuf_insert(struct mbuf *, size_t, const void *, size_t);
----
-
-Inserts data at a specified offset in the Mbuf.
-
-Existing data will be shifted forwards and the buffer will
-be grown if necessary.
-Returns the number of bytes inserted. 
-