Changed version for 2.0 pre-alpha.
Changed version for 2.0 pre-alpha.

This version will break compatibility and adds new features so the
first number is changed. The second number is instead for minor changes
that do not add new features or break compatibility.

MatthewLM/cbitcoin,MatthewLM/cbitcoin,1d4Nf6/cbitcoin,01BTC10/cbitcoin