Add DefProp, GetHeapptr, PushHeapptr, RequireHeapptr.
Add DefProp, GetHeapptr, PushHeapptr, RequireHeapptr.

All 1.1.0 functions that probably don't have as much use in Go programs
using duktape as they might in C, but may as well expose them.

olebedev/go-duktape,fattenap/go-duktape,jmptrader/go-duktape,mosolovsa/go-duktape,fattenap/go-duktape,jmptrader/go-duktape