add SDF.print(), allow inplace for SDF.update() and SDF.to_topic()

[tim-quix]

• Added SDF.print(pretty: bool, metadata: bool), which prints the value, and optionally metadata
• Enables SDF.print(), SDF.update() and SDF.to_topic() to be used without reassigning them (and you can chain them as normal)

sdf = SDF()
sdf = sdf.apply(a_func)
sdf.update(other_func).print(metadata=True).to_topic(my_topic)