Remove unneeded dependencies on resourcet and conduit.

Even though they may be transitive dependencies, they're not direct
dependencies, so they don't need to be specified on this cabal file.
Whitespace.
Take an http-client Manager as argument.

Instead of hardcoding withManager, which creates then destroys a connection
pool, this commit allows users to maintain a single, long-lived HTTP connection pool
that is shared between calls to this (and others!) libraries.
Major version bump per PVP.
Bump dependencies to accept latest versions.