Add mbuf_append_and_free() and mbuf_move()

CL: Add mbuf_append_and_free() and mbuf_move()

PUBLISHED_FROM=bdf73906dd93b2ebeace160596508e15480b54b4

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

@@ -0,0 +1,13 @@
+---
+title: "mbuf_append_and_free()"
+decl_name: "mbuf_append_and_free"
+symbol_kind: "func"
+signature: |
+  size_t mbuf_append_and_free(struct mbuf *, void *data, size_t data_size);
+---
+
+Appends data to the Mbuf and frees it (data must be heap-allocated).
+
+Returns the number of bytes appended or 0 if out of memory.
+data is freed irrespective of return value. 
+