Add support for verifying address

[Allen Farris]

This can be done via the "decodeAddress" API call. Status should be "success" if the address is valid, but version and stream number should also be checked. Here are some other values possible for "status": 'checksumfailed', 'invalidcharacters', 'versiontoohigh'

[Scott King]

I use this in my fork, got rid of eval() and numerous other things. Feel free to check it out at https://github.com/Lvl4Sword/PyBitmessage-CLI