class_docstr: torch.jit.script optimised Swish w/ memory-efficient checkpoint
  Inspired by conversation btw Jeremy Howard & Adam Pazske
  https://twitter.com/jeremyphoward/status/1188251041835315200
code: def symbolic(g, x):
      return g.op("Mul", x, g.op("Sigmoid", x))
  
imports: import torch
  from torch import nn
  from torch.nn import functional
label_desc: Use image node_id 1 for calling the SwishJitAutoFn obj's underlying member method code with example usage: obj.symbolic(g, x) and returns: g