1. Rename 'interpret' -> 'interpretP' in Control.MonadPlus.Operational
2. Add 'fromProgram*' functions that translate programs into stronger types
Merge branch 'master' of https://github.com/sacundim/free-operational
Refactor the 'Operational' class so that 'ProgramT instr m' can be an instance.
Rewrite 'liftProgram' in terms of 'interpret'.
More reworking:

1. Introduce Control.Operational.Instruction and generify the
   instruction interpretation to over there.

2. Introduce 'interpretTM' and 'interpretM' for
   Control.Monad.Trans.Operational.

3. Arrangement and documentation tweaks.
Minor doc tweaks
Bump version up to 0.2.0.0, and add more info to the .cabal file.