Disconnects Store state fields from Compiler (#1761)

*  Moves CodeMemory, VMInterrupts and SignatureRegistry from Compiler
*  CompiledModule holds CodeMemory and GdbJitImageRegistration
*  Store keeps track of its JIT code
*  Makes "jit_int.rs" stuff Send+Sync
*  Adds the threads example.

examples/fib-debug/main.c

@@ -71,7 +71,7 @@ int main(int argc, const char* argv[]) {
   printf("Instantiating module...\n");
   wasm_instance_t* instance = NULL;
   wasm_trap_t *trap = NULL;
-  error = wasmtime_instance_new(module, NULL, 0, &instance, &trap);
+  error = wasmtime_instance_new(store, module, NULL, 0, &instance, &trap);
   if (error != NULL || trap != NULL)
     exit_with_error("failed to instantiate", error, trap);
   wasm_module_delete(module);