Prettier Show instance for RLP items
Move the main RLP package to a nested package and reexport it

I don't like that folks have to import two packages to do RLP stuff, and
I want the namespacing for the converter stuff as well, so this should
be nicer.
Rename AsRLP to RLP.Convert
RLPConvert and asRLP -> converter

Reads better, and makes the connection between the two more obvious.
Renaming and munging in RLP.Convert API

Overall I feel better about this.