Cli

Added a minimally functional cli.

running 'sia-cli' will do nothing, because by default it tries to bootstrap to the network and download all of the existing blocks. Luke will have to fill out this part of the code.

running 'sia-cli genesis' will create a new wallet and a genesis state with the wallet's coin address as the genesis coin address.

Once the wallet is running, you can choose to mine by pressing 'm', you can print the status of the wallet by pressing 'p' (this will print out all addresses), you can send coins to an address by pressing 's'.

afaict, once the broadcast stuff is done everything except file storage will be complete in the cli, at least as far as a beta is concerned. My current plan is to finish up the whitepaper, and then to pass that onto Luke. While Luke finalizes the whitepaper draft, I'll add all of the storage stuff to the cli.