Move callback guest out of direct examples dir

examples/callback-guest/README.md

@@ -0,0 +1,5 @@
+# Call back guest
+
+This is part of the `callback` example.  This Wasm module passes host imports and its own functions to the Wasm host to execute.
+
+See `examples/callback.rs` for the host

examples/callback.rs

@@ -3,7 +3,7 @@
 use wasmer_runtime::{compile_with, compiler_for_backend, func, imports, Backend, Ctx};
 use wasmer_runtime_core::{structures::TypedIndex, types::TableIndex};
 
-static WASM: &'static str = "examples/callback-guest.wasm";
+static WASM: &'static str = "examples/callback-guest/callback-guest.wasm";
 
 /// This function matches our arbitrarily decided callback signature
 /// in this example we'll only call functions that take no arguments and return one value