This PR adresses #166
Error handling in wallet was ported to failure in https://github.com/mimblewimble/grin/pull/713
Using the same error model makes wallet code simpler and may simplify migration to Hyper.
* Bump up crates versions
* Finally add a Cargo.lock to avoid dependency breakages
* Build doc update for testnet2
* Fix test framework not really using its mining config
* Testnet2 genesis, best so far at 128 difficulty (a nice number)
* Minor build doc update