Turn TCPv4 into a real FLOW by including the module within it.

Note that this changeset isn't for merging -- we should make this
change in V2, but this saves a bunch of diffs by experimenting in
V1 first.
Add a Conduit configuration to initalize `Conduit_mirage`
Adapt Conduit code generation to improve interfaces
Add Conduit deps
Add Resolver interfaces
Partial sync of V2.mli with V1.mli
Remove the dependency on Conduit and just copy the poly variants
bump working version to 2.0.0
Merge pull request #291 from avsm/make-tcp-a-real-flow

Bump to Mirage 2 and add Conduit/Resolver interfaces