shachain: switch encode/decode methods to use io.Reader/Writer
shachain: switch encode/decode methods to use io.Reader/Writer

* Help avoid a bug related to passing a copy of bytes.Buffer into
Encode/Decode instead of a pointer

aakselrod/lnd,aakselrod/lnd,BitfuryLightning/lnd,bryanvu/lnd,ddustin/lnd,ddustin/lnd,AndrewSamokhvalov/lnd,LightningNetwork/lnd,LightningNetwork/lnd,BitfuryLightning/lnd,AndrewSamokhvalov/lnd,bryanvu/lnd