Rename all tool modules to Tool_*, and their directory to "tool"
Drop wrapped_pubkey type for now

The "p" property is specific to finite fields anyway, so there is no
gain in abstracting the group element type in it.
Exporting make_{read,write} was a bad idea

They do not behave as expected on serialized JSON objects. Instead,
directly export a reader and a writer as needed.
Add a generic group parsing module

Move code specific to a group implementation there, and use it
everywhere else.